1997 Pontiac Sunfire brakes lock up

have you checked you back breaks for wear. or looked at the drums. maybe try replacing your self adjesters. and that should stop them from locking up

This is because the shop that replaced your brake shoes do not have the correct arc. I have seen these many times. In the morning, the rear brakes will actually lock up hard on you, correct? Replace the brake shoes with riveted original shoes and you'll be fine.