I have a 1994 F350 CC Dually 460 4.10 gears full Banks. Pretty much 75% tow vehicle with heavy fiver. (only use it for trailer towing, but once at the campground it is used to sightsee - hence the 75% and not 95%) I have a spreadsheet that I track mileage "hand" calculated from mile/day one. The average over it's entire life (50k miles), per the spreadsheet, is 7.64. I drive it easy, taking my time getting up to speed and then topping out at 60'ish with OD locked out. MT my highest was 11.1 driving 55mph. Average MT is 10.12. Average for actual towing miles is 6.68. Lowest reading is 3.72. LOL My truck is still pretty much showroom new. Over its 20-year life, it has NEVER let me down.