11 inch brake problems!!!

need some advice on a problem with the super bee's brakes A12 car,power brakes, 11 in drums, all rebuilt, new wheel cylinders, new master and booster, skimmed drums,new lines. brakes were working fine for about 6 months driving, they now have developed a problem with the brake pedal sticking to the floor a little bit... the brakes are not locking up but they do grab and pull you to a stop brake return spring is fine,i've adjusted them up but still same problem seems to be getting worse each day now, what should i look at first, i'm thinking master,or wheel cylinders

sticking master cylinder, or booster, or some link in that area

Since this is a handling oriented forum I would suggest the problem is that they are drums, might be time for discs.

Relevant advice, pull each drum and inspect the insides. I suspect an issue there.

Bad poppet valve in the booster...repair/replace.