Gooseneck fifth wheel and a flat bed. Help!

It did start with the 11" brakes on the truck. I removed a 1-ton single wheel rear with 13" brakes from a donor truck and used the springs from it. I have also added a little more spring to it as I have a close friend that runs and automotive spring shop. This is an odd truck as it has a 4spd with a 3.42 gear. it is a K20 and I have installed a Dana 60 front axle due to it having a 10 bolt factory axle. I have know clue what the gvwr is on the truck at this point. I know that with my 26' deck over gooseneck with my 240 skid steer the truck squats about 2" versus my '97 powerstroke that squats about 4.5". I built the truck to pull with and be able to use on the farm, the truck drives good enough I would just assume to pull a camper with it than I would my powerstroke. The issue I am running into is I have only pulled bumper pull campers. Never hooked to a fifth wheel, the camper I pulled was from Raleigh NC to Yadkinville for my cousin. I did have a weight distribution hitch and a sway control but with this truck being a single cab long bed from the factory it did ok but did not like the 32' travel trailer on the highway at 65-70 MPH. I don't want to have a fifth wheel that starts the old saying of the tail wagging the dog.