1976 3/4ton 4x4 Shortbed

[l79m20]

Sooooooo..........last post was about getting the rear cylinders on and having a full pedal. Well thats all true, until you start the truck, and then the pedal is gone, turn truck off, pedal pumps back up and is fine. Thought the booster was bad, so took a known good one off a parts truck and replaced it. Same issue. Did some searching on the net and saw some people saying the proportioning valve had to be adjusted. Turn key on, press in adjuster on the valve and then bleed. Tried that with no significant results. I am hoping someone can shed some light on my issues.