First thing go to the towing chart that trailer life has and look up your equipment on the truck. This will be a good reference for max towing with fifth wheel. This weight is everything. Stuff people etc.
On the trailer side. If you have a local dealer work with them and check with bbb on complaints etc. then do research on what you want in a fifth wheel.
We got a canyon trail 33FRLQ from gulfstream last summer and it has been everything we wanted and more. We have 4 slides and are very heavy 13K with stuff included. We have a 2004 6.0 and it works to tow this rig.
Good luck in your search. It took us several years to locate one with the floor plan we wanted.