Is it a disc brake or drum brake car? The boosters are different. Do you have a car with 15+ inches of vacuum? Even a new car. Run a long hose from that car to the booster on the GTX and see what it does.
But I will say that your booster is,bad, and the master is not causing this problem.
You might try removing the booster and run in them as manual brakes.
Booster Dewey is the place to go for booster rebuild.
It is a disc brake car. When the weather improves enough (foot of snow on the ground now) I'll put another car along side and see what happens then. Thanks for the suggestion.
