I'll share my experience - perhaps it will help. I had a similar issue when I switched out the front rotors and calipers on my truck. Front disc brakes would tighten up after a few blocks. Had me and couple of good mechanics stumped !
It turned out to be a combination of problems. The rear drums need to be adjusted properly as they activate first ( piston in M/C opens rear circuit first ). Getting the rears right, allows you to fine tune the travel on the push rod from the booster to the M/C. Piston needs to return to correct position when pedal released in order for fluid to flow back into the M/C, and take pressure off front brake lines. You should also have a residual pressure valve installed on the rear line, as well as proportioning valve. If you are concerned with your proportioning valve, I'd replace it. ( Not too expensive )
