New 5th wheel doesn't tow well

IBcarguy wrote:
I just bought a brand new Jayco Eagle HT 30.5 MBOK. Unloaded weight is 9635 lbs, max loaded is 11950 lbs. Dry hitch weight is 1795. Optional 16" wheels with Goodyear tires.
My TV is a stock 2013 GMC Sierra 2500HD 6.5' bed, crew cab, 4x4, Duramax diesel. The truck has plenty of pulling power and the rig sits nearly level when hooked up.
The problem is that when you hit a rough spot or dip in the road, the trailer "chuggs" (for lack of a better word) back and forth until the road smooths out again. It does not seem to bounce up and down... it's more of a lateral bumping back and forth. We went on our first outing yesterday, about 2 hour drive and it wore me out! I could never take a long trip like this.
The truck has a B&W goose neck with the removable ball in the floor of the bed. I installed a Andersen Ultimate hitch with the upper ball adapter to the pin box.
I know this problem has been brought up before and there could be a number of causes and corrections. Any suggestions short of replacing EVERYTHING to fix this problem?

Do you have the Andersen hitch correctly torqued down to the bed. I would you put the pin weight on the truck and then re-torque it to 50 lbs.

The two side bolts get torqued to 40 lbs.

Also check to see if your GM bed is humped in the middle front to back like others have noted, and that the hitch is flat to the floor.

Chris