I have an '88 4spd. 2wd 1/2 ton with 22R carb'd. I just moved from Nebraska to Tennessee with my truck loaded down plus pulling a trailer that was completely full. It was a very heavy load, but my truck pulled it okay. I maintained about 60-65 mph on the interstate (about 55 mph up steep inclines), and averaged about 22-23 mpg. It would have gone faster than 65, but I didn't want to push my truck too hard. I'll put a picture below.
Whatever you get, make sure before you leave for your trip that it is in good running condition and that the load in the truck and trailer is balanced properly about the axles. It makes all the difference.
Good luck with your move, and here's that pic: