I have a 20 and would expect better mileage pulling that. I pulled a 3,000lb trailer empty one way 300 miles and loaded with 8,000lbs so 11,000lbs total the other way. I got about 14mpg average for both. It’s still pretty new but you should get better. If you haven’t changed the oil I would do that and a fuel filter to be safe. I just started using Hotshot Secret EDT and it made my engine a little quieter. I think it’s increasing my MPG by about 5% but too early to tell. I’m going to switch to AMSOIL next change too.

 

Hunter
I did just have the oil changed I will be on the road again next Friday I can only hope I get a improvement I’m running a injector cleaner and boost every other tank full maybe two then the third the additive
Thanks

 

I averaged around 12mpg hauling my Lance 975 at around 4200 lbs loaded and ready to camp. I was always in 6th and rarely downshifted. Does your truck stay in 10th at highway speeds on flat terrain?

 

Bozdx
I see you have 2019 I believe they made some changes to the Duramax engine in model years 2020 and 2021 I’m letting the transmission do the work I have used the tow haul switch. I haven’t noticed which gear the transmission has stayed in
Thanks

 

The engine (L5P) is the same from 2017 through 2021. The transmission is the only thing different starting in 20.

Assuming a 20% tongue weight on your previous 5th wheel, the 3500lb truck camper should be roughly the same payload for your truck. Is the 3500lb the dry weight of the truck camper? I'm wondering if you are putting a much higher payload on the truck than you would have if it was the 5th wheel.

11.5mpg is still low, I agree. Do you have any mileage data for just the truck itself without any payload?

 

The truck camper is the wet weight including us passenger weight for our payload weight I would estimate we might be 1800 lbs more payload vs the pin box weight of the 5th wheel If I could figure out how to download pictures to the site I could show you photos of my 2008 setup vs the down sized Truck Camper The Truck Camper has a far super aerodynamic design then the 5th wheel Im super dissatisfied in my fuel economy Thanks $75000 dollars poorer I should have kept my 2008 Duramax Unloaded on the 2021 I am getting 19-21mpg

 

Hello, and welcome @Gnsolman2021 ,
To attach a picture, tap the little picture icon under the text entry box when you're writing your posts. Tap the popup and that should open your gallery.

 

There ya go! Gorgeous truck, that red is nice.

Actually, I think the aerodynamics are worse with the bed camper. I dunno, but I think the air is getting caught up by the shelf over the cab where your 5th wheel was more in the wake of your truck.

 

That is a sweet setup! Is that the 9-6 or 10-2 Northern lite? The truck looks awesome, I love the new High Country trims. I used to like the new Denali grill better but I have to say that I favor the High Country now.

I would just go and enjoy your truck and TC and not sweat it. Hopefully you don't have buyer's remorse...

 

That is a sweet setup! Is that the 9-6 or 10-2 Northern lite? The truck looks awesome, I love the new High Country trims. I used to like the new Denali grill better but I have to say that I favor the High Country now.

I would just go and enjoy your truck and TC and not sweat it. Hopefully you don't have buyer's remorse...

 

I pulled my 12k 5th wheel from northern Utah to Houston. I ran 9.5 to 11.5 depending on the hills and speed. That was with 1500 miles on the truck. I am up to 4500 miles and empty I get around 21 mpg on the freeway.

 

Don't know if this helps or not but my LMM mileage continued to improve until I got about 15k on the truck.

JD makes a lot of great points regarding drag coefficients and such.

The best that I have ever gotten towing my 5vr weighing in at 15k and 13'6" high is 10.5 towing at 65 MPH, normally it is only 10 MPG. At 70 MPH the fuel mileage drops to 8.5 to 9 MPG depending on grade and wind.

 

It is a 8-11 Wet Bath I didn’t want a 8ft truck bed to accommodate the 10-2 some remorse on the truck. In general I like the truck and all of it new technology I made the mistake of calculating the lose in fuel mileage over a 100,000 miles We will pay $5000 more in fuel cost on top of the $75,000 we have into the new truck. Big dent in the wallet Eventually I’ll get over that an enjoy it. Keeping my figures crossed one of the replies said their mileage improved at about 15K. Time will tell
Thanks

 

Did my first decent tow this week in the '21 up fly fishing in North Central PA. Cruise set at 64 MPH on the way up was 9.4mpg and on the way home not using cruise but same speed was 10.4mpg. Mostly nothing flat on the whole route. New RV is a 40' at about 15K lbs. Old setup was 34' RV at about 11K lbs and same run I would easily do 11.5 to 12 mpg with the '17 6 speed.

Not terribly happy but what I noticed is that the 10 speed when your running flat would be at about 1300 RPM versus 1700 RPM with the six speed. When you go up any sort of hills with the 10 speed you down shift and you get to 1900 RPM where the 6 speed would grunt up those same hills. That shift happens like clock work. I'm guessing part of that is the weight of the trailer itself meaning the older truck pulling same speed would have to down shift as well. What I'm thinking though is that a difference of 600 RPM shouldn't equate to just one gear and if the 10 speed would use an in between gear on the smaller hills then the MPG would increase. Cruising at 1300 RPM when it's flat and the first sign of a hill bang your up to 1900 RPM. I'll have to check the manual mode to see what it says but in this regard the 10 speed is not so great.

On the other hand with no RV going back and forth to fishing spots I was getting almost 17 mpg and I would say that it is more like city traffic . Not to many stop signs but driving between 35 and 45 mpg on dirt roads. At these speeds I was running down around 1100 rpm so in this regard the 10 speed is working great.

Wrapping it up, it appears to me that with the current programming the 10 speed doesn't give any performance or mpg gains while towing. Honestly I would be happy with my old 6-speed back. In some conditions the 10 speed works fine but it doesn't in others. Could it be optimized to give gains throughout the operating range? Yes I think so.

 

Did my first decent tow this week in the '21 up fly fishing in North Central PA. Cruise set at 64 MPH on the way up was 9.4mpg and on the way home not using cruise but same speed was 10.4mpg. Mostly nothing flat on the whole route. New RV is a 40' at about 15K lbs. Old setup was 34' RV at about 11K lbs and same run I would easily do 11.5 to 12 mpg with the '17 6 speed.

Not terribly happy but what I noticed is that the 10 speed when your running flat would be at about 1300 RPM versus 1700 RPM with the six speed. When you go up any sort of hills with the 10 speed you down shift and you get to 1900 RPM where the 6 speed would grunt up those same hills. That shift happens like clock work. I'm guessing part of that is the weight of the trailer itself meaning the older truck pulling same speed would have to down shift as well. What I'm thinking though is that a difference of 600 RPM shouldn't equate to just one gear and if the 10 speed would use an in between gear on the smaller hills then the MPG would increase. Cruising at 1300 RPM when it's flat and the first sign of a hill bang your up to 1900 RPM. I'll have to check the manual mode to see what it says but in this regard the 10 speed is not so great.

On the other hand with no RV going back and forth to fishing spots I was getting almost 17 mpg and I would say that it is more like city traffic . Not to many stop signs but driving between 35 and 45 mpg on dirt roads. At these speeds I was running down around 1100 rpm so in this regard the 10 speed is working great.

Wrapping it up, it appears to me that with the current programming the 10 speed doesn't give any performance or mpg gains while towing. Honestly I would be happy with my old 6-speed back. In some conditions the 10 speed works fine but it doesn't in others. Could it be optimized to give gains throughout the operating range? Yes I think so.

I wonder if you try locking out 10th gear what it would do to your mpg. Running that low of RPM seems like you're asking to lug the motor. That's why on the 6sp we lock out 6th gear and only run up to 5th for highway driving while towing. If there's a large hill coming I downshift it to 4th to make sure my RPM are above 2k before I am starting to climb. These trucks really like 2k rpm under a load, and I don't think the newer versions of the L5P are much different in that respect compared to my 2017 L5P. My LMM was the same way; lock out 6th and the truck did better with temps and fuel economy.

 

I have a 2020 HC 8 foot bed SRW pulling a 36ft FW at 14K and 13’2” tall. Average 9.5 to 11 depending on headwinds, grade changes (mountains or flat road). Running between 65 and 70 mph interstate. Wet weight on truck is right at the 12,250 lb GVW with total weight RV+truck 22.4K. Unloaded on a trip of 700 + miles mixed roads (interstate, secondary) was 23 mpg. Truck has a Rolling / retractable aluminum bed cover.
Jeff B

 

You can still be lazy with it; just shift to M and up to 5. I think you'll be happier pulling that big beast.

 

I've tried that and what I didn't like was that it won't do the aggressive downshifting when I'm on the brakes which means the exhaust brake functionality isn't as good. I had to manually downshift it to get the same exhaust braking effect. Maybe I'm missing something?

 

...................

Now I feel like I should try it without manual mode to see if there's a difference in how the EB works.

 

Yeah, try it and let me know what you think. I can't recall the EB behavior in manual mode with cruise control enabled but I know that it works flawlessly in automatic. But without CC, the EB functionality was definitely better in automatic mode because with light but continuous brake pressure it will downshift very aggressively. In manual mode there is no such automatic downshifting. Of course all of that functionality is controlled in software; a shame we can't tune these things...

 

Pretty sure I experienced what JD is describing with the LML too. About the only time I used M mode was descending mountains with a load. Then I could easily pop it down a notch as needed. Better than letting the computer do it since it would command 3rd and highway speed and show me some RPM's that I did not want to see.

All the rest of the time it was just normal D mode for me. That '12 would pull a big 5er most anywhere anytime in 6th all day long. I checked over hundreds of miles of the same load and same route and saw no difference dropping to 5th.

Also that torque management crap is a bit overdone on some trucks. I remember putting the old 6.0L in my '07 in 4L to get a load to move then have to stop and go back to 2H. I hope the new 6.6 gas has a little less TM. It's pretty sad when a new 3500 won't move the same load that you had no problem moving with your '78 C-10 gas burner with a 4spd and a crappy clutch. LOL

 

I never locked out 6th gear in the other trucks I had, why would I do that???

Your not lugging a diesel when it is at it's peak torque range of 1600 RPM and in fact I like to run it at that range. Peak torque is peak efficiency. I might add that driving it like that gave me near 12 mpg depending on route run on my LBZ and darn close or at it on my 2017. Mix of two trailers on the LBZ and the '17 always pulled the 11k fifth wheel.

If you run outside of peak torque your either wasting fuel or getting more heat, and usually the two go hand in hand, choose your poison. Power is never free more fuel , more power more heat because we never really change the efficiency of these motors and what we can't convert to mechanical energy is lost in heat.

Your also not getting the same Exhaust Brake functionality by running it in Manual Mode.

 

Here's my 2-cents on your mileage issue with the Truck Camper. We jumped from a 2017 2500HD Duramax to a 2021 about 6 months ago and my loaded and unloaded mileage (at the pump calculated) is the same; 6-spd versus 10-spd but smoother shifting. RPM difference is about 100 @ 65 mph; lower with 10-spd. Our speed odometer reads 2 mph fast; therefore, 67 mph indicated is actual 65 off GPS and 1450 RPM's. As mentioned earlier, peak torque is at 1600 RPM's and that's where diesel like to run. Speed is our economy's worst enemy as aero dynamics really play a part. Empty like other mentioned, is 19-20 mpg @ 65 mph. We carry a hard-wall 7' wide full bed length (7') camper dry weight of 2100 pounds and tow behind a Chevrolet Colorado ZR2 (2.8l diesel) for off roading. Mileage with camper alone averages 13.5 mpg between Nevada and Michigan @ 65 mph. When we had our 'pop-up' truck camper the average was 15.0 mpg @ 65 mph. That 18" taller over cab and rear drag cut mileage 1.5 mpg. When we tow a 'loaded' (6K lbs) Colorado 4 wheels down, our average is 10.5 -11.5 mpg and most of our travels are Nevada and Arizona mountains. I use Manual and Exhaust Brake all the time to down shift through the gears and not touch the brakes until I'm down to 25 mph. I don't use tow-haul as my load doesn't need the shift pattern difference. My air-dam between the cab and camper overhang made a big difference in cab noise reduction but did not affect mpg (look close to see it). By the way, 2020 did bring some changes to the LP5 engine and chassis on the 2500 HD. Larger drive shaft to put more torque to the wheels in 1st gear along with other internal engine beefed up parts. This article is lengthy but covers what most owners don't know about the changes: 6.6L L5P Duramax Specs, Tow Ratings, And Model Year Changes (dieselresource.com)
Happy Camping everyone!

 

Here's my 2-cents on your mileage issue with the Truck Camper. We jumped from a 2017 2500HD Duramax to a 2021 about 6 months ago and my loaded and unloaded mileage (at the pump calculated) is the same; 6-spd versus 10-spd but smoother shifting. RPM difference is about 100 @ 65 mph; lower with 10-spd. Our speed odometer reads 2 mph fast; therefore, 67 mph indicated is actual 65 off GPS and 1450 RPM's. As mentioned earlier, peak torque is at 1600 RPM's and that's where diesel like to run. Speed is our economy's worst enemy as aero dynamics really play a part. Empty like other mentioned, is 19-20 mpg @ 65 mph. We carry a hard-wall 7' wide full bed length (7') camper dry weight of 2100 pounds and tow behind a Chevrolet Colorado ZR2 (2.8l diesel) for off roading. Mileage with camper alone averages 13.5 mpg between Nevada and Michigan @ 65 mph. When we had our 'pop-up' truck camper the average was 15.0 mpg @ 65 mph. That 18" taller over cab and rear drag cut mileage 1.5 mpg. When we tow a 'loaded' (6K lbs) Colorado 4 wheels down, our average is 10.5 -11.5 mpg and most of our travels are Nevada and Arizona mountains. I use Manual and Exhaust Brake all the time to down shift through the gears and not touch the brakes until I'm down to 25 mph. I don't use tow-haul as my load doesn't need the shift pattern difference. My air-dam between the cab and camper overhang made a big difference in cab noise reduction but did not affect mpg (look close to see it). By the way, 2020 did bring some changes to the LP5 engine and chassis on the 2500 HD. Larger drive shaft to put more torque to the wheels in 1st gear along with other internal engine beefed up parts. This article is lengthy but covers what most owners don't know about the changes: 6.6L L5P Duramax Specs, Tow Ratings, And Model Year Changes (dieselresource.com)
Happy Camping everyone!

You sir need to tell more about both trucks you have. Big Duramax and Baby Duramax! Love it!

 

Little premature to be complaining about fuel mileage on a new truck, especially when towing.
Your comparing a broke in Engine, to a new one. Give it sometime.
You also changed your setup, going from a fifth wheel to a slide in, I personally believe the aerodynamics are worse with a slide in, but there in theory should be more rolling resistance with a fifth wheel with two extra axles on the ground behind the truck.


Sent from my iPhone using Tapatalk

 

I just got done towing 17,000lbs on a 2020 3500HD Duramax and over 500 miles averaged 8.7mpg. 8.2 was the lowest and 8.9 was the highest for the trip. Truck has 6,000 miles on it. Filled the tank 3x. Wasn't thrilled about that. About 1/4 of the trip was mountains, 1/4 rush hour traffic, the rest wide open 60-65mph. I'm hoping this isn't the norm.

 

Sounds about right to me.

My GCW is just shy of 28k and at 60 mph I average about 9 mpg. But I have a 50 gallon auxiliary fuel tank in addition to the 36 gallon onboard tank so I can go 600+ miles between fillups (easily a full day of driving). If you're going to be putting in significant mileage with that rig I highly recommend a similar setup.

I saw from the other thread that your truck is SRW and that you're new to towing. I highly recommend setting up the "weigh my truck" app on your phone and taking a ride over the nearest CAT scale to get your weights. But first, give this thread a good once-over. Happy towing!

 

The payload on my dually is 5300lbs.

 

I'm not sure where you're getting your numbers, but the bolded portion of the quote above is very wrong. The only trucks with payload values on the order of 7500 lbs are class 4 and 5 DRWs running 19.5-inch wheels and tires. I am nearly certain there aren't any 3500 DRWs with payload numbers that high. Your SRW truck's payload is probably just under 4000.

Please post your scale ticket. Your truck's RGAWR and tire capacity is probably 7250 lbs, and I suspect that with your trailer hooked on you're slightly over that value already.

We're dumping this truck for a bigger one. Any suggestions as I'm looking to buy in next few days.

 

Cp4 is in ‘19 and ‘20 rams and ‘11 - CURRENT Fords.

 

Quick update to a previous conversation in this thread: Since we last talked about it, I have started just leaving the truck in D for towing the camper and letting it do its thing instead of locking out 6th gear. Truck runs just fine, and I got a small bump in mpg towing the camper. Nothing to write home about, but statistically significant in my opinion.

On one trip I do have 2 large grades that I will pre-shift the truck before to help maintain speed a little further up the grade. But other than that the 6speed Allison just does what it needs to without complaining. No temp concerns on the trans, oil, or engine coolant, and no EGT issues.

For reference, camper has a sticker weight of 13k. Still haven't gotten over a scale with it.

 

FWIW I run my rig in "D" as well at about 28k GCW, often on grades, and I've never had any issues.

 

As do I with my 13k 5er. I have found the exhaust brake works much better in D and it has no problem downshifting on its own when needing it to pull a grade.

 

We probably average the same MPG with our 2021 Silverado 3500 SRW with WolfCreek 840 camper, but it also depends on speed and hills. I've seen a low of 9.5 mpg with a strong headwind on mountain roads, and have taken side roads keeping it under 65 instead of the freeway where possible, we've seen up to 14.5 mpg. Driving the freeway at 80 mpg kills the fuel economy with our Duramax, loaded or unloaded. Unloaded I've averaged just under 20 mpg round trip by avoiding the freeway so we could drive under 65. Will warn you about the factory tires, we had a blowout earlier this month, the RR tire blew doing 65 on a mountain road, and Goodyear was nice enough to credit us 50% the price of a new tire, which I just picked up. Upgraded the tires today, and will be selling the Wranglers soon on Craigslist. The tire shop manager said I should be able to get $800, since the used tires only had 6700 miles on them, at 11/32 depth (the new tire is 12/32). Nice rig!

 

Wow that tire!

 

Just saw your post. I have a 2022 3500 Duramax diesel and pull a 5th wheel but only 32ft long and 9000lb loaded. I got a bunch of data to generate the table below. I basically lose 52% versus not towing at any speed.

These are MPG's from the DIC (truck's trip gauge) and don't include regen periods. Some folks say these figures are optimistic and actual MPG is lower than what the truck says. However, I did eight partial fill-ups over 1400 miles and found the DIC figures matched very well with the manual calcs (miles/gallons) to within 1% so I think they are accurate. Hope this helps!