Slow Returning Brake Pedal Driving me nuts.

None of the rest of the system should have anything to do with the master returning. I would say this is all right in the area of the linkage, binding, etc, the master, sticking or other defect, or something wrong in the booster.

Not sure I'm about to explain this well, but there is no possible way, that the tiny 3/16 tubing and long runs in such as my big 'ol 2500 long bed big cab Cummins can return as fast as the master, AND that restriction is sorta why you can "pump up" the pedal if there's a little too much movement, AKA the rear drums out of adjustment or whatever. When you stab the master, you should be able to almost immediately give it another pump

This could even be as simple as one of the master piston springs broken, etc