What kind of Gas Mileage, is normal?

[Realism]

What kind of gas mileage is considered normal for our trucks.
I have a 2020 GMC Sierra 1500 SLT 5.3L V8 10 speed
I know the V8 does do more gas and I dont expect it to pull 19 mpg in town. But I have been averaging like 12-13 mpg. Yes most of my driving is in town with like 15 miles a few times a week on the freeway.
For a Truck that was touted as 22 highway 16 in town and 19 average. I feel very let down by what I am getting in mpg.
I dont haul large loads, I have All terrain tires and not the all seasons I usually got for my envoy, but I wouldnt think that would hit the fuel cost that much.
Im also very easy and grandpa ish when it comes to driving, so no hard take offs or anything foolish.

Is there something I am missing? This just feels like the trucks of the 90s where 10-12 mpg was average for a work truck.

 

[Mooseman]

Is this calculated or from the on-board computer? Sometimes they can be off but usually not by much.

Are the start/stop and AFM operational? Although they don't affect MPG that much, it could be something that's contributing. Other than that, check the usual suspects like an intake or vacuum leak, air filter, dirty MAF, lazy O2 sensors.

 

[Mooseman]

You sure you have the 10 speed and not the 8 speed? IIRC, it was only available with the LM2 diesel until 2022. Try shifting manually until you get to the highest gear.

 

[Realism]

Is this calculated or from the on-board computer? Sometimes they can be off but usually not by much.

Are the start/stop and AFM operational? Although they don't affect MPG that much, it could be something that's contributing. Other than that, check the usual suspects like an intake or vacuum leak, air filter, dirty MAF, lazy O2 sensors.

Start stop functions, though I prefer to have it off. I run the AC right now so it doesnt shut off anyways. AFM, I have no clue how to check that. Intake seems good. No leaks that I can hear or detect just casually.. Air filter is clean, MAF, didnt check that, but doubt it. Havent checked O2 sensors on my scanner at all, doubt there would be anything wrong with it.
The vehicle is a certified one, so dealership went over it with a fine tooth comb before selling it.

Pretty sure it is a 10 speed. The Manufacturer sheet was in it and the vin matches up, and the sheet lists it as a 10 speed. Plus the shifting is super smooth, Cant even tell really, unlike a 6 and 8.
I will try a manual shift at some time tomorrow.

Also its from looking at the DIC, I will hand calculate it out next fill up, but it seems about right with cursory maths. Im filling up about every 4-5 days instead of my customary once a week or week and a half with my envoy. and that had a smaller tank and got better mileage.

 

[Mooseman]

I asked about start/stop and AFM in case they had been tuned out. On the MPG page of the DIC, it should say how many cylinders it's running on. May also help to keep it on the instant MPG page so you can monitor your driving habits and can see what your average is doing.

 

[Realism]

MPG page on my DIC doesnt say anything about how many cylinders are running.