Reading back over the thread a bit, wondering if the vacum source(s) are representative of the throttle state. The vacum to the brake servo is always there, regardless of throttle position. You need a vacum source that is dependant on the throttle being closed, .so, that's after the throttle body?
Just my thoughts, I'm not an expert.
Suggest keeping boost low 'till you get it under control.
Mac.