A$$ walking. LOL. I just finished a fairly major (for me) overhaul of my rear suspension. The only things I didn't touch were the parking brakes and rear wheel bearings. The rear end was shifting about on the highway like a belly dancer. Not doing it now though
. My shocks were shot and the subframe bushings were too, but the trailing arm bushings came out easily and looked almost new, so I don't think the shifting about was due to the trailing arm bushings. (I torqued them under load and now my rear wheels are visibly cambered positive
I should have left them alone)
The only problem with throwing the kitchen sink at it like I did is now I can't tell you what is exactly keeping it stable. But I can't see how those little plastic things could cause the a$$ walk very much (but I have been wrong before).
FYI the subframe bushings can be installed with the subframe on the car if you can get the old ones out.