If it's rear drum, I'm thinking it's weak springs not releasing fully. I'd open the rear drums back up, take 'er apart, use compressed air (wear a mask!) to blow everything clean, and replace every spring, washer, and hardware bit in there.
Discs? I don't know enough about them "new fangled" things to offer an opinion. In my day, we stopped a car with our feet...and we LIKED IT!
C.J.