Unstable handling

04 Prerunner xtra cab at highway speed becomes very unstable and sways when going thru a dip or a bump on the road. Had into several Toyota Dealer shops, they verify; yes there is a problem. Unable to isolate and repair. Replaced rack, lower ball joints, struts, shocks and several 4 wheel alignments. I still have the problem. Is there anybody out there with the same problem and found the fix?

 

My guess would be to check all the bushings in the suspension and steering, if that hasn't been done already. I hear that a bad bushing can be difficult to locate.

Hard to believe that more than one professional shop hasn't fixed it yet. They did make a lot of money off of you, though, replacing perfectly good parts