In a pickup based MDT, I suppose there's the F450 and Dodge's cab and chassis 4500 and 5500. The GM 4500 and 5500's I'm not too sure about. I've talked to owners who traded out pretty quickly.
If I recall correctly if you go 6500 you can get the Cat C7 or Cummins ISB? The F650 with Cummins or Cat might also be a possiblity.
I really like the business class M2 Freightliners. They cost twice what a pickup based truck does, but would probably last twice as long.
For the same money or less, though, you could probably find a used HDT with hundreds of thousands of miles left (especially towing RV trailers). Make sure to have a mechanic inspect it, and do the dyno run. I guess they can also measure crankcase blowby.
Talking to a few guys who have gone that route, HDT's seem to get better MPG's than I would have thought, and you would never want for more power or stability.
Dodge Ram dually laramie 4x4 w/jake, B&W, Brakesmart.
Kit Patio Hauler 394F toyhauler 5th wheel
Camo 680 Rincon, Green 500 Foreman, Blk twincam Roadking