My 5th wheel shudders violently when towing.

I have a 2015 GMC 2500HD Crew Cab diesel with a B&W turnover ball hitch and a B&W companion hitch towing a 2006 Cedar Creek Silverback 29LRLBS (unloaded weight of 10,070 lbs. The hitch was installed by the dealer who I purchased the camper from and who sells and installs many hitches and trailers. It seems any change in velocity while I'm traveling results in significant shaking of the truck even violent shaking at times. Anything from getting into the throttle quickly, to the transmission downshifting while slowing for a stop sign or even a bump while maintaining speed causes the issue. Sometimes when I'm slowing and the truck downshifts I even have to get out of the brakes just to help settle it down. I've taken it back to the dealer twice. I've spent a lot of time with the installers trying to trouble shoot and it's a head scratcher. We briefly towed another camper of similar size and type and it seems to do it with another camper. They are pointing towards flex in the base plate for the B&W hitch. I'm not sure. We even put a gooseneck adapter on the camper and took it for a short test drive and it actually improved the ride quality slightly. I've searched the interweb and I've called B&W and nothing... I think I've exhausted all avenues that the dealer is able/willing to provide so naturally I'm here crying on the forums. Anybody got any ideas or contacts to fix this? Thanks in advance.