I'm the newbie around here when it comes to diesels... Mine is (and from what I've heard and read will always be) a stock 6.4, 5spd Auto, 3.73 gears, 20" wheels. I'm only at 1400 miles on the truck. The best I've seen so far is around 17mpg at 65. I'm averaging around 14.5 in my commuting... half of that is at 75, some is at 65, and some is in-town. I have been adding PS (I think that's what it's called) fuel treatment/cetane boost.

Haven't towed anything yet...