New Owner with a Herky Jerky Ride! Help!

I have been lurking here for a couple of months and my wife and I decided to take the plunge and buy a Trailmanor! We picked up our used 98 2518 yesterday. We love it! It is a really sweet camper and we look forward to going camping.

We do have a big concern with towing it though. We have an 05 Honda Odyssey which can easily tow this lightweight trailer. Honda put in the coolers we need and the dealer installed a Reese Class III hitch with a 6000 lb WDH.

However, when we travel on the highway with concrete seams in it (most highways in PA!), the van gives a herky jerky, front and back movement at speeds over 40-45 mph! It is so bad that you can't speak right! If the road is smooth asphalt, it doesn't happen, only on bad concrete roads with evenly spaced seams.

The dealer drove around with us and thought that much of what we felt was normal. They did replace the brake shoes, check the drums and bearings, and install a new plug (to be sure there wasn't an electrical problem with the brakes). This didn't help. They also took the chains on the WDH up one link to move the weight a little more forward. This helped a little.

Any ideas? I don't think we could drive more than an hour is the van is going to be jerking around like this.

Could this be some weird harmonic thing going on? Will this hurt the transmission?

Thanks,

Dean