4th gens have a three link rear suspension. Thats a torque arm (long arm that runs down the middle of the car, attached to rear end and transmission mount or aftermarket chassis brace mounted), keeps the axle housing from spinning when power is applied, and two lower control arms, one at each end of the axle, keeps the axle from moving forward/backwards. Panhard bar at the back of the axle that runs from drivers side of axle to passenger side of chassis, keeps the axle from moving left/right.

You have an aftermarket 9" rear end (stock these have GM 7.5" 10 bolt rear ends) with an aftermarket torque arm and aftermarket adjustable lower control arms with poly bushings. Rear swaybar looks stock with stock endlinks.
Looks like your shocks and springs are not stock either. Springs are red right?
The grey shocks might be comp engineering (drag) shocks.
Get a power washer under that thing