I'll be shopping for a new (or new-ish) truck shortly for pulling a medium size trailer or 5th wheel. It seems like the vast majority of 3/4 and 1 ton trucks around here are 4WD, with jut a few 2WD...
Important consideration: If you pull a travel trailer rather than a 5th wheel, you'll be very surprised how easy it is in 2WD to be unable to get moving uphill from a stop on even a slightly slippery surface. Not so much with a 5th wheel because you've got more of your weight on the truck.