New 5th wheel doesn't tow well

I've always thought more about the trailer's suspension with chucking when we had our 5'ers. The chucking you feel is the trailer bouncing. Not enough to see but enough to feel. Trailer suspension is unusually stiff so shocks on the trailer may or may not help. Trailer tires are usually filled to max sidewall pressure and bounce on uneven roadways like concrete highways. Nothing you do to the truck is going to stop it. A shock absorbing hitch or pinbox is likely the best you can do. We just lived with it as part of towing a 5th wheel.