We have a 25' 04 Safari and was towing with a 1500
Dodge Ram using a Reese WD, with a High Performace Sway, using#1200 WD bars and we also experianced the concete Shake, Rattle and Roll. We recently upgraded our TV to a 2500 GMC and at the same time, lowered our WD bars to #800. Recently we towed over the same ( St. Cloud, Mn to Clearwater, Mn) concrete road and had very little of the Shakes. I can't say if the difference was from the truck or the lower rated WD bars. Whatever it was it made a big difference.You might want to check out your WD bars and see if they're rated to high, for your setup.