With 3/4 ton trucks and fifth wheels, payload of the truck is usually the limiting factor. Once you decided what fifth wheel you want, use the gvwr of that fifth wheel as the starting point to decide what size truck you need.
The loaded pin weight of most fifth wheels will be 20 percent of the loaded weight of the trailer. You will want a truck with payload rating that can accommodate the weight of passengers, gear in cab, gear in bed, hitch (say 250 lbs) and loaded pin weight.
Ignore the dry weight posted in rv brochures and do not listen to salespeople. Use gvwr as the measuring stick.
My experience is that any fifth wheel with gvwr over 11k is suited for a SRW 1 ton. Over 13k is suited for DRW 1 ton.
If you plan on full timing or traveling extensive, a 1 ton DRW is recommended for fifth wheel Towing.