My 6.2 (in a 6400 lb Blazer) with a banks turbo and no OD with 4.10's and 36's gets anywhere from 15-19 mpg. I got 16 avg. over 500 miles in a week of driving during elk season including about 300 of that on the highway at 65-70 mph, the rest on dirt in 1rst and 2nd gear (moving average was 28 mph by GPS). Usually see 17 and a halfish commuting 10 miles each way in 45-50 mph traffic with 10 or so stoplights, and some city driving on each end. When it was stock it got between 19-23.