Well...
I'd go with a 4x4 RC. I've never found a situation where I would rather have a 2wd truck. The old man's truck pulled 21mpg, so I figure a nice, light 4x4 RC oughta be able to pull that. We went 4-wheeler riding and with the random snowstorm that dumped on us while in PA this weekend, and the crappy-ass place we parked/camped at, I'm glad we had 4x4.
My only real decision is whether to make it an auto or a stick. I hate autos with a passion(an extreme passion), but the old lady refuses to even attempt to drive my truck. After driving 12 total hours this weekend I wouldn't mind someone else being able to drive a bit.
Maybe just keep a 2wd and a 4x4 Cummins frame around and swap the body for whatever the situation calls for.