I have had my shackle bolts come loose on my TG front lift causing death wobbles. I have also had all of my bushing go bad after one run. The quality of the bushing is CRUD. I ordered new bushings because they claim that the new ones dont have that problem, we will see.
If it is rocking I would hazard to guess shocks, possibly steering geometry. Not sure if the shackle will cause the problems you are having.
Is it a rocking like on a boat? or a lateral shift as if the body slides from east to west while the tires stay planted?