What to try next??? dragging brake shoes

Heres what is happening after driving a short distance, stop and go traffic for instance, the right rear drum brake starts to drag, not lock-up but drag enough that the drum gets so hot it baked the paint off, and smokes, now it did this before I replaced the following and is still doing it: new brake drum cylinders, new brake shoes, all new ss lines, and new proportionary block, I have disc brakes on the front, the master cylinder is still power brake and was also replaced OEM . anyone with ideas??