is the car a 2dr coupe or boxtop?
are the tires at the correct pressures?
what condition are your shocks in, are they worn-out? are they for this car or something else, does the car bounce a lot?
are the upper & lower control arm bushings in good shape?
are the rear springs correct for the car and in good condition? does the car lean/sag, or have a lot of movment?
is the car raised in the rear or is at stock ride height? if it is raised too high, this can put the driveline in an awkward postion and invite wheel hop on a 4 link suspension, in effect it increases the angles and reduces control.
are the rear spring insulators still there and not worn-out?
one tire fire or limited slip? one wheel peels can take their toll on the control arm bushings.
do you have a rear anti roll bar?
with the parking brake set, does the diff rock when the car is pushed back & forth?
is there a lot of movement when pushed side to side?
this should keep you busy for a while, sometimes it's real easy to overlook the small stuff. remember these cars are over 30 years old, so they are going to need a bit of work on arthritic joints.