North Dakota Boy
Now i don't know ls1 as good as some of you other guys but i do know that 6.0l get bad mileage in trucks cause the trucks come with 4.10s. i know a guy personally that has an 8.1l big block and gets 3 mpg better mileage in an idetical truck but the big block has 3.73s and he averages around 15mpg wearas his old truck averaged 12 and he also hauls a skidsteer everyday that weighs 15000 lbs. Now maybe its just the trucks and maybe the 6.0l corvettes and gtos are different i don't really know. But being from ND state, 95 % of the people i know own alteast 3 trucks and 75% of them own 6.0l 3/4 ton chevys and i even own a 6.0l but in a denali truck and i get 17mpg on the highway all the time if i go 70 mph while they make 10 to 12 but it also has different gearing because its not really meant to pull that much stuff and is AWD.
I do know many others that have experienced horrible mileage with the 6.0l but i'm a pretty strong believer its because of the gears so my advice would be just make sure you got the right gears and i'm sure you'll be fine. i'm mean the new corvettes make 400hp and get 27mpg, now thats also a corvette but i'm sure either one will suit your need. and from what i've seen the 6.0l can be a little cheaper and easier to find but thats hear in ND state where trucks are everywhere. but good luck in your desision. i will be making the same one soon hopefully.