Probably so. First 600 miles on the truck I averaged 14.5. All highway 75-85 mph. Haven’t had a chance to pull yet since it’s shop bound already. Have a 43’ 5th wheel. Around 13k. I was hoping for around 10mpg pulling it

 

Ur not going to get 10 honest mpg pulling that trailer. You’ll be lucky to get 8

 

Yep. These things get wore every year. My 01 got 15 towing. My 07 got 13 towing same load. My 15 got 10. My 19 got 8. Now the 2021 is 7. But I guess that’s better for the environment burning twice as much fuel

 

It is frustrating. I just traded in my 06 Cummins for this 2021. I got about 12-13 pulling my trailer whether flat or through the Rockies. I knew I’d be taking a hit with efficiency with this new truck. Bought it mostly for the 100,000mile warranty and piece of mind. Hopefully after this first hiccup it will run flawlessly for at least 50k miles

 

I recently upgraded from a very tired 02 LB7 Dmax to a 2021 CC DRW.
My truck is generally hooked to a trailer nearly full time pulling up to 20klbs.
So far I am less than impressed with the fuel mileage.
My 02 pulling the same trailer and load averaged 11-14, empty it would do around 17-18.
My new truck is averaging around 6.4 doing the same thing, it also burned around 6 gallons of DEF in 1000 miles, which seems high compared to my off-road DEF burning machines.
I did do a 400 mile trip unloaded and hit 14.5mpg, which my 02 would have hit with a light trailer...

Just wondering what others are experiencing, I like the truck but the fuel efficiency hurts.
I have a bulk tank with on road diesel I fill from, so all of my fuel between the 2 trucks I am comparing are from the same source. Everything is hand calc'd, but the DTC has been nearly spot on so far.

I’m getting 15.2mpg on my 2020 silverado the last 24000 miles. I could get 23.5 at 70 with no wind in FL(flat) terrain. I love it, way cheaper on fuel compared to 7-9 mpg using a 1500.

 

DEF level/range 'indicator' seems to have 'issues', and the dealers don't seem to fill def tanks, so unless you filled it yourself it may not be using as much as it appears.

(factory doesn't fill fuel or def; probably a good thing for the trucks that sit on the lot for a long time - even though that doesn't seem to happen much recently)

 

So I do believe some of the changes in fuel economy have to do with the weight/aerodynamics of the new truck. These things are huge now, with this massive billboard front grill, that I am sure at speed is the equivalent of a semi truck in a hurricane. Also, with great power comes great fuel consumption. Not only to make power, but to condition the exhaust and perform regens on the DPF.

I get about 12 mpg towing my 7,000 lb Lance trailer. My 2018 Cummins got about 11 mpg with the same trailer. Our Sequoia got 10.5 this past weekend towing the same trailer. By that metric, it would probably take about 200,000 miles of towing for the $11k upgrade on the diesel to pay itself off... Sad to say, you might get a few fraction points better MPG as the truck wears in, but it won't likely be whole-number improvements.

I will say towing with the new duramax is a totally different game. At 20k lbs, I would think the new truck is much more comfortable, stable, and 'safe' feeling with that load than your '02 was. I used to tow around 8,000 lbs with an '04 Powerstroke and would never want to go back to that way of life. Out here in Oregon we have to go up and over 7 different mountain passes to get from where I live to anywhere north. To go south, you have to go over Siskiyou summit - not fun at all with old iron in the winter with a trailer.

 

This is my 2020 2500 with 35x12.50-20 Ridge Grapplers my GPS because of the larger tires to be off show this to be off by 1.9%. This is a pic I took a couple of months ago to show the the mpg with miles on the truck. This includes some load hauling and extended idle sessions at the ranch in NM and driving on the ranch in 4wd some 4wd low. The 2nd pic is what I get no load flat terrain 50 mile average.

 

Just did a 900 mile trip from NY to GA. Mostly flat road. Drove overnight, left new years day, so zero traffic for 98% of the way. Bed was filled with stuff, probably 800lbs of gear. 4 people in the cab. Cruise control for almost the whole trip.
At 80-85mph I got a pretty consistent 18mpg... for some sections that I had to stay at or below 65mph, it jumped up to 23mpg. That was measured by actual miles driven and fuel fill ups calculated.
For one section I was at 55mph for 10 miles, dash display said I was getting 24.5mpg.

So my truck (2500 CCSB 4x4) is very speed dependent for decent mileage. If I keep a calm foot on the skinny pedal, I can keep it in the low 20’s without trying hard. But as I get into the upper end of the speed range, the economy takes a dive and will cost at least 5mpg or more.

 

I would also add that you need to let the truck break-in. I don’t think you will end up getting the same mileage pulling but will get close. That’s what has been sacrificed for emissions and far more power. Empty you will able to get to around the same. The good news is towing 20k lbs around that often you will break in pretty quickly.

I‘m getting better mileage than my ‘15 LML empty and getting the same mileage towing 2500 lbs more on our new travel trailer that is taller and longer, so technically saw improvement there as well.

 

I have a 2020 SRW 3500 and tow an 18K pound average trailer frequently. I tow at 74 mph on the interstates and I bounce right at 11 mpg. sometimes 11.4, sometimes 10.6 but it is steady. I had the same truck in a 2019 and it did about 1 mpg less than the 2020 does, same trailer and same loads.

 

Ur not going to get 10 honest mpg pulling that trailer. You’ll be lucky to get 8

Lol “Opinions May vary” as they say.

Got the truck back today. We’re headed from SC to LA first. Then LA to TX, then TX to AZ. Going to have put about 3000 towing miles on the truck by 3/1. I’ll hit a scale somewhere along the way and update here what mileage I get on the dash and by calculation.

 

I pulled a 12k trailer from northern Utah to Houston, TX. Worst mileage going over the Rockies was 9.5 and averaged about 11. Best empty is 27, average about 22 highway and 14.5 city. I have about 3500 miles on the truck.

 

I recently upgraded from a very tired 02 LB7 Dmax to a 2021 CC DRW.
My truck is generally hooked to a trailer nearly full time pulling up to 20klbs.
So far I am less than impressed with the fuel mileage.
My 02 pulling the same trailer and load averaged 11-14, empty it would do around 17-18.
My new truck is averaging around 6.4 doing the same thing, it also burned around 6 gallons of DEF in 1000 miles, which seems high compared to my off-road DEF burning machines.
I did do a 400 mile trip unloaded and hit 14.5mpg, which my 02 would have hit with a light trailer...

Just wondering what others are experiencing, I like the truck but the fuel efficiency hurts.
I have a bulk tank with on road diesel I fill from, so all of my fuel between the 2 trucks I am comparing are from the same source. Everything is hand calc'd, but the DTC has been nearly spot on so far.

Yes these new diesels not very good loaded my 2020 Denali gets 8.5 with my 14k fifth wheel in tow. But empty i have got 19.5 at 75 on highway. Yes loaded i am using about 5 gallons DEF in 800 miles. What i get for buying a new diesel.

 

I just bought one drove home from Colorado 1380 miles I got 680 miles on first tank and second got me home. Right at 33 gallons put me at 20.5 mpg. Got it home driving around town it gets around 8 can’t believe it would tank that much around town my 16 deleted in 37 got 14 in town but I’m looking at getting Duramax tuner tuning anyone here running it?

 

My DRW gets 25 highway 19 city KAP

Nah 17 highway, literally 0 city lol

 

A big consideration in towing mileage is also the height of the trailer being towed. I got a slight "no you don't" on my mileage claim from someone's crystal ball. If the ball wasn't cloudy they would have seen that the trailer I pull is 10'3" from ground to roof with a molded front cap to aid in aerodynamics. Yes I pull the weight but I am not dragging a big billboard behind, I have roughly 16" from ground to bottom of trailer and this also helps as it does not have a large turbulence under the trailer as well.

I see these newer 5th wheels going down the highway that have 3 feet underneath of them and are pushing the 13'6" height to the max and I just think that they must be able to see the fuel gauge moving as they drive, and forget it if you had a head wind.

I figure all of my mileage by hand I know how much fuel my wife has paid for and how many miles I have driven !!

 

I recently upgraded my 2017 SRW 2500 to a 2021 SRW 2500. Thinking that was a mistake. My 2017 loaded, unloaded, towing always got around 20-21. Worst mileage I think I ever got was 17.5 and that was with a 2500# Lance cab over in the box towing a trailer with two RzRs on a 1600 mile trip back and forth to Moab. Loved that truck so thought I’d be happy upgrading to a new one. Driven 1600 mostly highway miles and I am averaging 15.3. empty. I drove about 150 miles today slight wind and got 12, empty. Super disappointed! My 2017 was my first diesel and first GM. I was mistaken to assume a new one would perform as good if not better.

 

I bought Duramax tuner emissions tuning Friday so I’ll report back how that goes on my 21 Denali long bed. Evidently it’s going to be California legal this year because it’s 10% cleaner burning then stock so I was told. So hopefully I’ll get not just power but mpg increase

 

The 20+ year model sit higher and have a bigger frontal area than the previous years. The drag is greater so the mileage may not be as good.

 

And they weigh more. I think my 2020 weighs about 600 lbs more stock than my ‘15 did.

 

600 lbs doesn't sound like a lot but it's like adding 2 refrigerators to your truck.

 

I did buy Duramax tuners emissions intact tuning and have been running it almost a week now. So before tuning truck did well 20.5-21 hywy hand calculated, in town horrible 9.4 was average and towing my 42 toy hauler was around 8 over all I could get 11-12 freeway around 63-64mph. Now tuned my mileage on hywy didn’t change much if at all I’d say just easier to maintain it. But towing I saw increase to 11 overall 13.5 around that 63mph mark. In town I’m seeing 12 unloaded. Hand calculated so far my dic is very close