Rear swaying on certain roads

Hi guys,
So I was driving on a section of 287 between Longmont and Berthoud Colorado when the rear of my 99 XJ started to sway back and forth bad enough for me to pull over and make sure I was not loosing one of the tires. I was going about 65 MPH when this happened. This section of road has those rain groves in it and are pretty deep. Other sections of this road also have those groves, but they have been warn down. I really did not notice the sway on those parts of 287. I came back home and checked the rear u-bolts and alignment pins. The pins looked straight and the u-bolts were a bit loose. I tightened everything up (probably over tightened the u-bolts a bit), went back up there and it did it again, but not as bad as the first time. The rear axle is the Chrysler 8 1/4 and it has the sway bar. The front sway bar is on this jeep as well. I just got new BFG Rugged Trail T/A P235/75R15 tires and Monroe Sensa-trac shocks. The Jeep has about 85,000 miles on it. The rear wheels aren't centered in the wheel wells and they look a bit cocked from side to side. I know the body panels could be a bit off, giving it the illusion of being cocked. The Jeep also has a trailer hitch, I don't know what the pervious owner was towing with it. Has this happened to anybody else, is it time for new rear springs, spring bushings?

sounds like it could be bad rear u-joint or out of balance ds....maybe tires need to be balanced

On those types of roads (including that one in particular) I feel as if the road is causing that swaying. I notice it in our jetta as well, not just the jeep.

-Joe

My wifes used to do that, with Goodyear 235/75 R 15 A/T's. I guess there was more going on than just the tires, but they seemed to make it worse.
I put the 235's M/T's off of my truck on hers (for winter to save the rim's) and much of the rocking disappeared. Mine where light truck tires and had a couple of extra plies in them, higher weight rating. I figured much of it was the relatively soft sidewalls in her Goodyear's.
I also found some side play in the leafs, front mounts (both sides). Tightened the bolts down a bit. The shackles seemed OK. The UCA's may be due for a change as well, a little play here and there, adds up.

Thanks guys. I was kinda thinking it was the road, as I do not feel the sway on ungroved roads. The combo of the tires and the road makes sense. I towed a couple of jet skis through that same section with the old tires and did not notice the swaying. I left the skis in Ft Collins and did not notice any sway on the way home.