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.

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.

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).

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???

Hello all, new to the site so if this has been answered I apologize. I purchased a 2021 AT4 1500 a few months back and have been looking at LED lights for the grill and wanted a 30" bar, love this install! Do you have any pix of the mounting and brackets you picked up from Depot? Of all things I am a service manager for a Ford store but we also own a GMC/Chevy store, figured I'd go to the dark side for a while, love the truck, just needs more lights. When I had my F-250's it was easy but not a lot of room to play here. Thanks in advance!