I had an old truck I redid the brakes on. Had a similar problem. When I took one of the junktion blocks loose from the brakeline, it had a solidified piece of crud in it. Fluid could slowly get through, but the harder I pushed the pedal, the more it blocked the passage. Other than that I would tighten the shoes until they lock up the hub. Then back the shoes off until you can just hear them rubbing the hub when you turn it.
