Truck ride with big toy hauler

we have a 38 foot all american sport toy hauler, the factory sticker says it weighs 14,000 pounds with an air pin box, pulled by a 1990 SRW 1 ton diesel dodge, it pulls well on the straight and level roads, but add a mountain pass and I'm down in first gear doing 30 MPH, we all so have an air ride hitch, so it rides over the bumps pretty well, but is this the right term "buck and chucking" is in there has to be a small amount of space between the pin and the clamping jaws, what I am trying to say its more of a forward and back movement that can be felt in the truck it drives me nuts, we have been looking at and plan to move up to a MDT, something like a freight liner sport chassis