31" tires @ 50lb, 3.73 gears, 700r4, vortec heads, flex-a-lite dual fans, tbi w/gm performance intake. I have heard some pretty outrageous claims on mileage for the 6.2, 20mpg sounds doable. I can get about 12.5 babying it on a steady cruise. It is usually a little less.Having the aerodynamics...