I'd check:

Wheel brgs for play, inspect rear suspension links, idler arm bushings for play and pull one of the bolts out of the steering dampener- it's likely dead or weak. Put a torque wrench on the 3 steering bolts and tighten(don't loosen them) box bolts, 65 ft-lb? I think that maybe right- theres a bulliten out on them.
Many of things to check.

Michael