Q: Can you help me figure out how to fix a wobble in my truck..

Ok.at slower speeds it seems to be fine. i can feel something that feels to be a small drag.at about 55mph or higher it wobbles horribly.i consider myself mechanically inclined so i did do a few checks and this is what i came up with.. ujoints are good.the back ujoints are new with no play.the front ujoints have no play either.the center support bearing and housing had a good bit of play so i replaced the bearing and hanger.so cnter support bearing is good.front ball joints, stablizer bar, bushings, wheel bearings, control arms ,hub assembly all seem to be good but as i was checking them pretty much rocking them all as much as possible i notice that the rear end is rocking back and forth (as in up and down) as i rock the truck.more down than anything. not just at the resr main but the entire rear end it seems.. as it drops naturally the driveshaft drops with it. i am talking like more than an inch.maybe even more than 2 inches.should i realign Ubolts and retighten them.

My car has 200000 miles.
My car has an automatic transmission.