AC Guru's, I need some help.

I second the suggestion about the evaporator core leaking. As suggested check your evaporator drain hose with the UV light (wear those yellow Elton John looking glasses too. They'll help you see it much better). You can also see if there is any UV dye in the water that drips out from it if you can't crawl under the car to get to the drain hose. Also look down in the vents with the light & in the heater duct for any traces of dye.
Also make certain the service valves aren't leaking. If you have a leak there it won't show up with a vacuum stability test because the gauge hoses are still hooked up & sealing the system.
DON'T USE STOP LEAK no matter what! It causes more problems than any good! (cue the guys that will say "I've used it in my car blah blah blah!")