I have an 02 F-350 Crewcab 4x4, but with the V-10. I get 14 mpg with a camper on it at 75 mph. It has the tow package, so if I slow down a bit I get much better mileage. My owner's manual shows the V-10 and the diesel as having the same towing capacity. I don't even feel most trailers behind me, although the ride does get better.
The Dodge 4-door is just an extended cab with a shorter front door to accomodate a back door. It does not have anywhere near the room of the Ford Super Duties. At least the Dodge 1500 doesn't - but aren't the 2500 and 3500 the same? I sat in the back of a new Dodge 4-door and it was cramped. My Ford is a lot more spacious.
I got the gas engine because of previous tranny problems with diesel trucks, both Ford and Chevy and having heard of Dodges with the same issue. Plus, my wife drives it most of the time around town, and I didn't want her trying to find a station with diesel fuel - not that many around town.