did you rough up the drum surfaces before reinstalling them?
in some cases having them turned and trued up a bit helps with that.
what sort of condition were the backing plates? those were notorious for wearing a pattern in the backing plate and that would actually keep the shoes from moving correctly. if the backing plate has ANY indention worn in it that would probably be the cause of your shoes hanging up creating the no brake power situation.

couple of things to ponder while scratching your head ;o)