Ladies and gentlemen! I am happy to bring this story to an end.
The problem was the intermediate pushrod between the booster and the MC. It was approximately 1/8” too long. This was not noticeable when bolting the MC to the booster during assembly. However, once the MC was bolted to the booster, the piston in the MC was pushed in 1/8” and no longer at the “home” position. That means the MC piston was never able to properly release pressure from the front lines. So pressure in the front brakes would just keep building.
I removed the intermediate rod and functionally shortened it by drilling out the center about 1/8” so the nipple on the booster rod had more room. Put it all back together. Test drive and NO MORE DRAGGING OF THE BRAKES!
