Slow Returning Brake Pedal Driving me nuts.

I have had this ongoing problem with my slow returning Brake pedal and locking up if I hit pedal to hard on my 73 Duster. I have thrown money at the problem after suggestions from many.

Had the Booster redbuilt
Swapped out the Original prop valve to an adjustable Willwood.
Recod master Cylinder from Rock Auto (couple years old now)
New hard lines
New Flexible Rubber Lines

The only thing I havent replaced is calipers and master cylinder. Should I go the whole hog and replace these as well. This is driving me crazy. Any help appreciated.