[Riwright]

Lots of good advice here.

One other thing you could look at would be resonance. If the trailer and tow vehicle are configured in a manner that it "likes" to chug then that would explain it. If you want to get technical with it you can google up "resonant frequency" but you don't have to.

It's easy to test. Just adjust the height of the ball a little bit.

Another thing to check would be tongue weight. If it's too heavy then the unibody could be flexing a little. You could take it back to The Car Show and see what they think. They are a really good dealer and I'm sure they'll help you out.