Looking at an '05 GMC 2500 6.0
 

Could some of you guys help me out here?. My son is wanting to buy a 2005 GMC 2500 4WD 6.0. It has 90,000 on it body is good no rust pretty clean. The main thing that concerns me is the fuel consumption. I am told 11 mpg is about the best it can do. Any powerchips that will help that? And the salesman told him it had an Allison transimmsion???? Is that true???
Appreciate any help.
LW

You are correct on the mileage...they aren't the best especially with the 4.10 rear end (it may be a 3.73). There really isn't much you can do with the mileage either...my best advice is save your money and don't buy any of the advertised gas mileage improvers. They don't work - been there done that. Just keep it maintained and drive it easy and that will get you all the mileage your gonna get out of it. Mine also did a little better with high test gas - especially when towing. Enough so that is was worth the little extra at the pump, but I did have a BlackBear computer in mine that called for the 93 octane. The transmission should be a 4L80E not an Allison. To my knowledge the only motor that has the Allison is the 8.1 liter (not all of them but most) and the Duramax. The 4L80E is still a real decent transmission in my opinion and mine still had the original one after 145,000 miles when I sold it. Hope this helps - Good Luck!

6.0 only has 4l80 (as mr shamrock said)... i've had 3 buddies buy 6.0 2500 hd's and they got between 10-14 mpg... 14 is optimistic and i wouldn't count on it. but they'll pull. honestly though if you're going to go that route and get that weak of gas mileage, i'd go 8.1

Thanks for the help men. Main reson he's interested in it is the price, we can get it for 8,000 I think. And we will need to do some towing. It has 4.10's. Only reason I wanted to talk to him out of it is he drives 60 miles round trip to work most days. I am afraid it will eat him up on buying fuel.
I dunno we'll see what we decide. It is a darn good truck for the money.
Thanks again
LW

Sounds like a good deal for a 4X4 with under 100K miles.