Is 5.3 fuel mileage really this bad?

[Cigarette1AT4]

I know most people use FB etc. other than posting on forums anymore but figured I'd ask anyway.  This is my first GM product since the early 90's when I had the old school Z71's etc.  I am a service manager at a Ford store outside of San Antonio (we also own a GMC/Chevy store) and given the demand for trucks, our GM at our other store had a buyer for my 2018 F250 that I couldn't pass up.  I don't really tow much anymore and my commute is only 4 miles to work (small town) each way, home and back for lunch etc.  I bought a super nice 2021 GMC AT4 1500 with the 5.3 in it, the mileage has always been "ehh" at best but I understand it's a truck, not looking for pie in the sky car fuel economy.  I have been averaging 13.3-13.6, lately it is now 12.3, is this really normal?  Truck has a leveling kit and 33's on it and even on the highway I am seeing sub 16 out of it 70-75 MPH, drive like a grandpa in town.  All my F-250's with 35's + have averaged 15-18, I had a 2018 F150 Ecoboost with 33's on it and averaged 17-18.  Normally I wouldn't complain too much but with the tiny gas tank and under 13 MPG I am losing my mind.  Have had my service manager at the other shop scan it and look at it, all normal, no issues...are they REALLY this bad, I can't even break 300 miles on a tank?  I ordered exhaust for it but I shouldn't have to be like a highschooler and add exhaust, programmers and CAI's to get a bump.  Thoughts???  

[swathdiver]

55 minutes ago, Cigarette1AT4 said:

I know most people use FB etc. other than posting on forums anymore but figured I'd ask anyway.  This is my first GM product since the early 90's when I had the old school Z71's etc.  I am a service manager at a Ford store outside of San Antonio (we also own a GMC/Chevy store) and given the demand for trucks, our GM at our other store had a buyer for my 2018 F250 that I couldn't pass up.  I don't really tow much anymore and my commute is only 4 miles to work (small town) each way, home and back for lunch etc.  I bought a super nice 2021 GMC AT4 1500 with the 5.3 in it, the mileage has always been "ehh" at best but I understand it's a truck, not looking for pie in the sky car fuel economy.  I have been averaging 13.3-13.6, lately it is now 12.3, is this really normal?  Truck has a leveling kit and 33's on it and even on the highway I am seeing sub 16 out of it 70-75 MPH, drive like a grandpa in town.  All my F-250's with 35's + have averaged 15-18, I had a 2018 F150 Ecoboost with 33's on it and averaged 17-18.  Normally I wouldn't complain too much but with the tiny gas tank and under 13 MPG I am losing my mind.  Have had my service manager at the other shop scan it and look at it, all normal, no issues...are they REALLY this bad, I can't even break 300 miles on a tank?  I ordered exhaust for it but I shouldn't have to be like a highschooler and add exhaust, programmers and CAI's to get a bump.  Thoughts???  

 

So does that take into account your work commute?  If so, I'd say that's pretty on par if a little low for a lifted truck on 33s.

[WeGone]

I'd say its the short commute, The longer the drive the better it should get.  

 

[Black02Silverado]

To me that sounds a little low, compared to what others are posting online and what I'm getting out of my stock 6.2.  Heck my stock 2002 would only get 15mpg for the most part so I would think you should at least get that.  Not sure where to look at getting better economy. 

[KARNUT]

My 02 Avalanche gets 14-15 in town with a 373.

[Cigarette1AT4]

I would usually agree with the short commute it dropping some but even on the highway I am 14-15...15.5 at best empty cruising 70-75, 80+ and you can watch it fall, I couldn't imagine a trailer hooked up to it.  Truck is bone stock right now, tiny 3:21 rear end (crazy, would have guessed it would have been taller) with the 10-speed, always downshifting to keep the speed...other than the leveling kit and 33's, I don't know if it is older technology with a pushrod motor vs. what I am used to working with the Fords but 1/2 ton to 1/2 ton, same tires, same size wheels, same clunky 10-speed, same leveling kit my 18 King Ranch F-150 would do 16+ on the same commute, granted it was the ecoboost but turbos drink fuel too always spooling with 3:73's.  I know when my dad was still alive he always drove Yukon Denali's with the 6.0 and I think 6.2 in the later ones and his wasn't this bad, it wasn't great but not this bad and he was in real estate stop and go all the time.

 

I guess this sounds about normal for the 5.3's, was hoping for around 15 in town, 18 on the highway which I think should be "doable" in today's pick-up market?  

 

Thanks for the replies gang, love the truck, just wish I could go a little further on a buck (or 3 lol).

[newdude]

Well, tire diameter wise you are in a stock diameter option.  Standard tire size on AT4 is 275/65R18 which is a 32" tire.  Optional are 275/60R20 which is a 33" tire.  Being it's got "33s" on it, they are most likely a lot wider than stock and I take it more aggressive, so there's a big fuel mileage hit right there.  The wheels are probably a lot heavier as well.

 

On your driver door jamb, look at the tire label and see what size the stock tire that came on it was supposed to be.  If it came with the 18"s, makes me wonder if the PO ever got something like the Range Pulsar module installed to correct the tire size.

 

Thing # 2 is its an AT4 and its leveled.  AT4 is already 2 inches taller than a regular Sierra, and doesn't have the lowest most air deflector like the regular Sierras.  Add another 2 inches to the front, lots of aerodynamic drag under the truck.

 

I think the wheels/tires and the level kit are what is hurting your mileage the most. 

 

Oh, being its 3:23 gears, try driving in manual mode at set the gear to L8 or L9 and see if it improves the mileage any.  If its hitting 10th, it could be lugging with the added rolling resistance and causing increased fuel consumption.  L8 or L9 will let the top gear be 8th or 9th that it can shift to, but will keep the power up more like the 3.73s did in your Ford.   

Edited January 17, 2022 by newdude

[voided3]

Lots of good advice given, but I'll add for comparison our '21 Silverado LT 5.3 4x4. It has the front air dam removed and I drive it in L7 (8-speed transmission) to disable DFM (and it just drives better that way, to me), but it's on the stock Michelin Primacy all-season tires aired up to 38 PSI and I run it on at least 89 octane, plus it has a hard tri-fold tonneau cover.

 

Details out of the way, I can squeak out 20 MPG on the highway with that setup. Towing a 3800 lbs. single axle travel trailer, I average 12-14 MPG.

[Cigarette1AT4]

Thanks for the comments all!  Newdude, it had 18's stock so if that is a 32 and I went to a 33 that shouldn't make too much difference.  20x9 on 33x12.5x20's like most everything on the road.  

I get being a little taller and tires bigger but I wasn't expecting it to be this bad is I guess my point when everything else I have driven it has had little to no effect on mileage, at least not this drastic.  It's not like I have that huge offset and stuff you see out there, tires and wheels are practically still tucked under the fenders.  Running a Nitto Ridgegrappler, pretty common for street queens lol.

 

I'll try the manual mode, I can see it lugging and hurting mileage.

[rbdjr]

Make sure alcohol content not to high, this time of year they like to mix in higher percentage of alcohol because not any other drivability s problems usually don’t show. Many times in the winter months I have measured 50% or higher of alcohol in my fuel, and never ran E85 or another , in NJ they must keep it lower than 14.99% and 9.9% at all times, so I know they mix it in, just by higher alcohol you lose miles per gallon as Alcohol has about 50% less BTU than normal unleaded fuel

[Byrds8]

A lot of different posts I have read here have said leveling it doesnt drop MPG too terribly much. However, those same post will say tires will kill your MPG. If you went from a stock 9" wide tire and went to a 12.5" tire, depending on the brand you chose, it could have added a lot of weight per tire. My Sierra SLT has stock 33's on it that are 40lbs each. There are some tires that are still stock size but weight 20lbs more each. That alone kill MPG without ever going up in size or width.

 

Plus, like rbdjr said, winter grade fuel sucks also.

[apierce918]

Seems a little low to me, that is what I get around town with a new trail boss and 6.2 L. I'm sure winter blend isn't helping as another poster said.

[CamGTP]

If they are LT Nitto's, those are heavy ass tires and much wider than stock. Going to tank the fuel mileage.

 

My truck is a little different but I get the same if not worse fuel mileage. Mine is a 2016 5.3/6 speed and it's lowered on stock 18's still, I get 14-15mpg in the summer and maybe 10mpg in the winter with 8 miles a day round trip to work. The short trips and very cold temps here in Minnesota ruin my fuel mileage. But I honestly don't care because it still takes me 14-18 days to burn through a tank.

Edited January 18, 2022 by CamGTP

[M1ck3y]

1 hour ago, Byrds8 said:

A lot of different posts I have read here have said leveling it doesnt drop MPG too terribly much. However, those same post will say tires will kill your MPG. If you went from a stock 9" wide tire and went to a 12.5" tire, depending on the brand you chose, it could have added a lot of weight per tire. My Sierra SLT has stock 33's on it that are 40lbs each. There are some tires that are still stock size but weight 20lbs more each. That alone kill MPG without ever going up in size or width.

 

Plus, like rbdjr said, winter grade fuel sucks also.

 

Larger diameter tires will generally improve highway mileage as long as they aren't excessively heavy. Reason being is that with the larger diameter, you have a larger contact patch. This result's in a distance further traveled for any given rpm.

 

City mpg's will tank, the extra weight and torque needed to get rolling in stop and go traffic favors small diameter tires. They're light, easily spin with little throttle input etc.

 

Deviating from stock tires is changing your gear ratio too; whether it be lower or higher. That's why lifted trucks with big tires are all about gears. 

[Cigarette1AT4]

Thanks again for all the replies, not often anymore you see a ton of replies on msg. boards, appreciate it!  It seems from what everyone is hinting too is this is pretty normal/average for the 5.3 (or 6.2 for sure).  I completely understand everyone leaning towards tires but this is the same tire and wheel combo I have run on all my 1/2 tons I've owned with leveling kits, nothing exotic or drastic but I guess it effects the GM's different than the Fords I've owned.  Same driving, same everything I would have expected a little better.  Like I mentioned in the beginning I know this is a truck and you don't buy a truck for fuel mileage but it seemed way off even from when it had the stock tires and wheels on it, only real noticeable difference with the stock tires was on the highway I would see 18-19 at cruise but now it is in the 14-15's, pretty drastic going down the highway empty cruising. I also got out my GPS and the speedo is dead nuts on with the GPS at any speed so I would assume unless GM's is calibrated by live GPS the overall tire diameter is having little to no effect.