Also you could possibly have a defective rear strut or spring. Tire cupping is typically suspension related if the wheel and tire are OK. Have them test the strut and check ride height.
The alignment shop can check the rear alignment relative to tracking with the front, toe-in, and camber (limited). If the camber is off they will elongate one of the strut holes and try to get it in, if off. If you have 16" wheels the camber is supposed to be -1.0 degrees. Rear toe-in/out is fully adjustable and should be .05" (1.5mm).
Thrasher CAI, DHP v1.0 PCM, SLP Headers,
3.25 SC pulley, CAIT GMAF, 2.5 DP/Hi-Flow CAT,
u-bend delete, 160 TS, ZZP Stage 1 72mm TB,
TB spacer, MSD 8.5mm wires, Autolite 103,
Goodyear Gatorback Serp. & SC Belt,
Nitto NT555R Drag Radials
1/4 ET: 13.210 sec. @ 104.490 mph
0 - 60 ft: 1.945 sec.