I've got a bone-stock '11 Crew, short-bx, 4x4, F-250 6.7L, 3:31. I don't really drive it around town so couldn't say what that mileage is. I recently pulled a 24' flatbed 1200mi. 600Mi empty, 600 W/a Honda Accord aboard. I ran ~80MPH the whole trip and averaged 11MPG.
Interstate system here is 75MPH so most run ~80ish.
@ ~73-75MPH with my ~3K# boat in tow I get 11-12MPG.
@ ~80MPH with just the truck I get 15-16MPG.
@ ~70MPH with just the truck I get 17-19 depending on the wind.
Fuel, oil, air, and oil filters is all I've done so far. I bought it new <100mi on it and I'm creeping up on 28K now. It's comfortable to drive and ride in, nice and quiet going down the road. DEF has been a non-issue for me despite living in ND. I keep a 2.5Gal jug @ home and make sure I'm full before any long trips and let the dealer top it off any time I get the oil changed. I was really hoping the mileage would be 2-3MPG better than it is, but 20MPG @ 80MPH isn't 3/4 pickup territory I guess. If I had any real issue it's that the fuel tank is only 26Gal due to the DEF eating up 5gal of capacity.
