Well here's another one to add to the list, it's doing this at startup:
YouTube - Grand Prix Startup Issue
I know, seems like a vac leak right? I sprayed the **** out of the engine with brake cleaner AND...nothing. Wtf.
Here's a couple videos on the shifting and vibration issues. The first one is an in-car, the camera didn't pick up much on the creak&snap noise it makes when I shift gears, but you can kind of hear how loudly the dash is vibrating. The second vid is an undercar shot of what happens when you shift it, the engine is doing the same thing if I were to get an under-hood video. Also during the last spark-plug swap we noticed the engine was offset toward the passenger side if that means anything.
YouTube - Shift and Vibration Problem
YouTube - Weird sound
AND...a quick video of a 20-50 pull, couldn't go much higher because I was in a 25. Used to have quite a bit more power, now it's not that great.
YouTube - Grand Prix GT Quick Pull