Does this happen on all roads, or just one in particular? On some road sections the expansion joints / bumps will be at just the right distance from one another that your setup will "porpoise" or rock up and down - but the next guy's rig might be just a little shorter or longer and will have little problem. Try slowing down a bit. I ran into this on I78 in Pennsylvania, it was incredible how the truck and trailer were moving with the dips - I thought the hitch would break off!
Similar to what Skipnchar posted, a quick way to "adjust" your setup is to move some weight around inside the trailer. I found that when I add just a little weight to the front by piling sleeping bags in the front of the trailer the ride and towing is better.
Your hitch is very adjustable. Read up on how to adjust it. It may need a major adjustment, or just something simple like using a different link when hooking up. Or it may need nothing at all, and just a small weight transfer in the TT and getting used to towing it is all you need to do.
Try different things and see how they work. And come back here to post what you do, as that may help the next guy!