Yes Sir! Your test subject will be ready and narrow your diagnoses in a few hours for sure. Happy hunting. Very interest as, the phantom issues resolved; are great stickies for the forums..Just re-read your post, put a check valve in the rubber line so it only reads boost no vacuum, the ball holds vacuum which may cause initialization error on subsequent startups, there's probably none left when the car sits overnight if it leaks out, easily verified by operating the vent lever after sitting overnight.
Make sure the ground is alone on that gauge as well, not shared by other gauges or lighting etc.
Plenty of good tests to do....