Did the alignment shop also align the rear of the car? The rear has to be aligned first and then the front wheels are aligned. Have the shop check for loose rear suspension bolts. Loose bolts will cause suspension to shift for and aft under acceleration and deceleration.
The rear end has no alignment adjustments. You have to pony up for adjustable camber arms, rod ends, or eccentric bolts. The camber arm bushings are usually the first to fail.