Not enough weight on the front of the trailer?? It's a fifth wheel, the pin weight on that trailer should be way more weight than what's on a bumper hitch! The OP would have to seriously overload the rear of that fifth wheel to achieve an unbalanced trailer.
My thoughts would be possibly chucking due to a solid pin box. He's got the right hitch for the job. Our first fifth had a solid pin box, we traded it off for a Montana. The Montana we had was our first trailer with the Morryde pin box. HUGE difference pulling the fifth wheel! Rode like a dream compared to the solid! Our Suites has the Morryde as well, we don't have any of that chucking or bucking or whatever you want to call it.
Dan