[NPRfan]

Three mechanics actually tested the rod tightness and one mechanic adjusted the length of the push rod into the master cyclinder. It is totally floppy (totally loose). I do not think that is the problem since several of us were aware that it could be a problem and we all checked it.
This is an unusual set up in that 99% of the time cars have the brake pedal push a rod into the booster which is attached to the master cyclinder. NOT HERE! Set up is: pedal rod into master cyclinder, 1 fluid line into booster, 1 fluid line out of booster to T splitter, T splitter has 2 lines out to proportional valve (1 front, 1 back), proportional valve has 3 lines out (2 to the front, 1 to the back).
The booster is currently at a 2nd local rebuilder shop. I do hope this solves the problem. What I'm looking for is confirmation that I was right in the first posting or if when I get the booster back and the system still locks up, the correct way to test the system to isolate the "locking or pressure retaining" part or dirty stuck valve or ????
If I get the booster back and the system still locks up, I will try to extend the pedal rod 10 inches to a position where I can install a new booster-2 chamber master cyclinder unit (current master cyclinder has only 1 chamber). I have 2 photos that pretty well show the position and connections if that will help. I tried to load the 2 photos but it is denying my effort. Sorry. I can email the photos directly to you if you wish.