I have just under 20,000 miles on the truck and the average mpg, pump to pump calculated, is about 7.6 mpg. Not too bad for a break in period. On one recently, I pulled 46K of roll stock paper from Arkansas to Omaha and got 7.4 mpg on that fill up, and that was after crawling I-540 and Hwy 71 from Ft. Smith to Joplin in the daytime with all the traffic. That 18 spd with 2.64 rears does pretty darn good on hard pulls, but I think the ported/coated manifold and larger BW turbo on that 500 hp 12.7 Series 60, with Walker megaflows on the stacks makes the biggest difference. It was in the high 90's that day, and when pulling the hills the EGT's stayed below 900F and I kept up to or passed every other truck on those hills. And there were some that told me this setup would be lousy for this. Oh well.