If the rear end was ever worked on the suspension arms may have been tightened while in droop on one side or vice versa if that side was tightened on an alignment rack. The change in position while tightening could also be the problem because of more or less bind on the high side. I would start y loosening every thing while on the alignment rack, bounce the car and re tighten everything at the ride height.
This is good advice. I will take slight issue though -
The Gen1 & Gen2 manuals require the suspension bushings (including the shocks) to be torqued to final spec with the car ballasted using about 400# of weight in the seats and trunk area. There is a factory spring-loaded bar that attaches to the wheel lips at BDC. This provides a repeatable reference plane that is independent of tire wear or height differences. Measure from the top of this reference plane to the bottom of the frame rails to insure that the frame is level relative to the wheels.
When the pivot bushings are torqued in the ballasted condition, they provide additional rebound control to the shock/spring system. I will tell you from experience that the difference in handling is dramatic when done this way vs anything else.
I will also add that it is quite difficult to get at some of the bolts with a torque wrench with the wheels on. Once I've got things ballasted & measured correctly, I pull the wheels at each end, put slip plates under each spindle and support the studs (with nuts on) with a jack stand. I carefully jounce the car a couple of times, then torque everything to spec.
There's so much variation in body panel alignment that I NEVER use bodywork for a suspension reference.
