2008 F250 Crew Cab Short Box, 5.4, 6-spd manual, 4x4, 140k.
2235 miles in 4 days. 85% highway, 10% city, 5% in 4x4 through a few inches of snow. On the highway, averaged 75-80mph. A couple hundred pounds of me and a couple hundred pounds of gear was the only cargo.
The only add-on that may (arguably) have helped with mileage is a tonneau cover (that failed in the last 200 miles).
Computer varied between 12.3mpg and 13.6mpg during the trip, but said 13.1mpg when I got home. Hand calculated, I got 13.4mpg for the whole trip.
A little better than I was expecting, but still no where near what I got on a very similar trip with my Duramax a few years ago. I think I averaged 21 or 22 mpg empty. But, the upfront savings of buying the gasser will still save me money in the long run, though.