Its been a near weekly topic lately so your not alone. Maybe it'll break in and improve some , but there are others fighting the same issue.

 

Mine is a 2021 no difference between 2020 to 2022 in the 6.6 dmax. I get about 12-14 towing and 18-20 empty on highways. My mileage started improving once the truck hit 10k miles. Letting the cruise control do most of the pedal control drastically helps mileage.

I use cruise control almost exclusively with no trailer and use it only after I hit my desired speed with a trailer to prevent hard acceleration as I tow horses. My previous 2003 5.3l gas silverado would get 12-14 in perfect conditions no trailer. I did not buy the truck because of mileage I got it to better control my horse trailer. My old truck struggled hard with a trailer and horses

 

Just picked up my 2022 on Friday from the dealer and getting about 15.8mpg unloaded. Of course it only has 156 miles on it.

 

You gotta wait a few thousand miles before it settles in! I'm at almost 4k now and have seen mileage going up nicely. Lots of threads on this, search around and you'll find this is the consensus.

 

Yes give it time. Get it fuel cost at or above $6 or even $7 a gallon we want all we can get.

Keep the tire inflated right, no hard acceleration, coast when you can, draft when you can, use cruse control, stay at truck speeds on the highway 45 to 65. Going over 65 and towing kills milage.

 

I have 12,000 mile on a 2022 3500 GMC Duramax, 10 speed 3:42 dually rear end 4x4, terrible mileage. 6.4 towing 8,000# ball tow RV. 14 running empty. Last 4,000 miles of mixed driving local, interstate towing and not, averaged 7.4 mpg. I replaced a GMC 2500 Duramax, 6 speed 3:73 gearing, got 9 to 11 towing same trailer and 19 to 21 at highway speed empty.
Wish I hadn't traded vehicles.
Dealers say nothing wrong, that just what they get. I get better mileage on 2005 dually with a 8.1 gas hog.

 

I have a the same issue with my 22 Silverado 3500 Dually 4x4 long bed, around 6 towing and empty highway around 13 MPG. I believe the emissions is to blame. If I remember right, the windows sticker says 21 highway. ?? I'm looking for mods to get better mileage.

 

Well I was driving empty today

getting 20 plus. Driving. 65 average cruise control

pictures to prove it. That was one way. On the way it was the same.

I am running a Banks Air Ram intake and filter. I was also driving in 1 lane and using cruise control. Staying at the speed limits when it was safe. I was not keeper up with Los Angeles traffic. I was purposely trying to stay near 60-65.

 

I’ll be taking my first “road trip” this week. I’m excited to see what it will really do. I’ll report back.

 

Yep, I have a short 100-mile trip coming up on Friday too, will see how mpg's go with the small rv in-tow and post it here!

 

22 L5P dually 4x4 3500. Just finished a 6500 mile ish trip out to western Canada. Not towing but about 2 k in the bed most of the trip.

Hand calc 19.1 mpg (US) for entire trip.

Still don't have 10k yet on the truck so it'll get better a bit.

With all the capabilities of this truck, my guess is GM put a lower priority on aero. The difference in mpg between 58, 60, 62, 65 and 68 is quite startling. Under 65, 20mpg is very doable. The 100 mile stretch I did at 58 was 24......at 68mph it's a 17 mpg truck at best. Even a slight headwind was noticeable on the mpg readout.

For the sake of my business, this truck will stay at 65 or less.

 

. The difference in mpg between 58, 60, 62, 65 and 68 is quite startling. Under 65, 20mpg is very doable. The 100 mile stretch I did at 58 was 24......

Your findings match my own, that between 55-60 the L5P sips fuel like a 3 liter Duramax. Start going faster though and it looks like you pay to play.

 

Headwinds and high speeds will zap the mpgs quite noticeably.
Personally, I’m a slow starting, cruise control using, coast everywhere I can, driving grampa. Rarely do I ever see over 60 as the aerodynamics on this beast don’t mesh well with higher speeds. The sweet spot in my 10spd is 48mph with cruise. 1100 rpm, 10th gear.
Routinely see balls deep into the 20s and have multiple trips (with good tailwinds haha) hang out in the low to mid 30’s.
Admittedly I’m out in SD and the altitude helps keep fuel use down and thinner air is a bit better for aero.

 

Headwinds and high speeds will zap the mpgs quite noticeably.
Personally, I’m a slow starting, cruise control using, coast everywhere I can, driving grampa. Rarely do I ever see over 60 as the aerodynamics on this beast don’t mesh well with higher speeds. The sweet spot in my 10spd is 48mph with cruise. 1100 rpm, 10th gear.
Routinely see balls deep into the 20s and have multiple trips (with good tailwinds haha) hang out in the low to mid 30’s.
Admittedly I’m out in SD and the altitude helps keep fuel use down and thinner air is a bit better for aero.

Wow, this kind of mileage has me foaming and drooling at the mouth here. I live in Utah, and with my 22 dirty max and A10 trans, I’m seeing 19 to 22 on an empty good day. But if I hook up the ole toy hauler (dry) with the RZR in the back, 7.8 mpg is the best this ole girl will see. And that my friend is on I-80 dropping down the sisters with the wind blazing down my rear. What if anything have you done gear wise or fuel wise for your numbers? Thank you sir for the assistance.
David F.

 

BC Canada. '18 L5P 3500 High Country with 178,000 Km on the clock, I just completed a 250 mile per leg, 500 mile total road trip with some town driving mixed in. No load but for luggage. I was seeing 24.25 mpg on the lie-ometer, backed up by readings from my Banks Derringer Supergauge fuel gauge of.74 percent remaining after each leg, in my 62 gallon tank, so the math matches. That's 9.5 liters/100 Km. (I had to fill up again before the second leg, just to believe what I was seeing and would it do the same thing on the way home!).
Being winter and the roads below freezing, I was traveling at 55 MPH mostly, with sections of 60 MPH and more. from time to time.
I don't know, but 24 miles per US gallon in a 7200+ lb truck seems pretty good to me.

 

From the trucking days: Find the LOWEST speed you can sustain in the highest gear available. This will likely be your best efficiency (fuel wise). My truck really digs the 49mph in 10th.
Yeah, I know. Not terribly safe for some roads, but where I live, I could do this all day long.
Usually in the mid to upper 20s for mpg, but have seen pretty consistent results that put me low to mid 30s. Winds are a huge factor on the mpg.

 

Be careful using that relocation kit from Banks, some on this site have found it clogs even faster since its recessed inside the adapter and has even less flow past the sensor which helps slightly to knock some of the soot off the sensor.
Just keep it cleaned and an extra sensor laying around in the event you break it while removing or cleaning it. I just pull mine every 5k and swap it with the other one, then take my time cleaning the one I pulled. I get 20mpg unloaded on the highway if I'm not driving it hard, about 15-16mpg with my ~3500lb boat/trailer. And in town, its not great with stop and go traffic, these trucks like a nice steady run on the highway.

 

Thanks for the info on the Banks relocation, I'll keep an eye on it. I plan to check on it after a long trip i have planned around 1400 miles.

 

Does it throw a code when you damage the sensor from cleaning? Any way to partially damage it or is it more of a go/nogo sensor?

 

If you disconnect the sensor without disconnecting the battery/s you may cause a code. the local auto parts store should be able to reset the code if you do not have a scan tool. It is possible to damage the sensor if you are not careful or use the wrong cleaner. I did not disconnect mine when I cleaned it.