depends on what year i guess. my friend had a 03 duramax and got 18+ driving it like a damn fool in the city and 20+ hwy. Traded it in on an 06 recently and it gets much much less in city and hwy.

 

i mean im not that worried about it but its just hard to believe. and i need a truck, i just wanted it to be a daily driver. and i figured 18mpg would be good but 10-11 thats just horrible

 

wonder why

 

I averaged 14-16 mpg's in my 1500HD depending on how I drove, this was completely stock.

 

A guy I work with has an 06 and swears he gets 16. Maybe ya'll got factory freaks. lol Everyone else I know with a stock LQ4 gets about the same as me regardless of it being a 1500HD, 2500HD of 3500.

 

My 03 1500HD, 2wd, averaged 12-13 mpg. This is with an Airaid intake, larger exhaust, 05 electric fans, a tune, and 3.73 gears. I think a lot of the poor mileage comes from the 4L80e and the fact you can do 60 mph in 1st gear(way too tall).

 

and almost 100mph in 2nd..

 

yeah on a good day driving highway i see about 17.. city driving forget about it i average about 9-10.

 

I have a 02 2500hd w/6.0/4l80E/265-75-16 tires and it gets 13-14 mpg on the highway. My friend has a 02 1500hd w/6.0/4l80e/ 305-70-16 tires and he averages about 9 mpg. When he got the truck it had 285-75-16 and it got about 10 mpg. My truck has 4.10 and his is 3.73. I have pulled trailers using both trucks(his had the 285 on) and mine is way stronger. I don't know if it is the gears or the truck itself. He has a hard time pulling hillls by itself and mine never comes out of lockup. His is in and out of lockup. Just thought that this would be a good comparsion.

BTW: Mine has stock airfilter and factory exhaust, his has k&n setup and true duals if that matters.

 

01WS6er, I've got the factory 245's on mine so probably a big difference than 285's/305's. (about 1.5" shorter) But mine never comes out of lockup. I hold OD up most inclines and just checked my last tank....11.4 mpg all in town, woot! lol I believe that the whole difference in your two trucks towing are the gearing and tire size. Both with identicle drive train, but the effective gear ratio is way different. Are they both 4x4 or 2WD? That will make a difference too if they are different.