When I get on it and shift hard it feels like the transmission is bouncing or moving around....during normal shifting its fine though. Im pretty sure its the tranny mount but its a brand new GM stock replacment...

Would the poly cure this?

 

Yes. The stock tranny mounts don't last very long if you beat on your car at all.

 

I had a friend with a 95 M6 and he was a power shiftin SOB, I would be sittin in the passenger seat and when he shifted that thing I would swear the console jumped a foot, I mean it came up hard.
This is the same guy who blasted the center section out of a 2001 M6 stock clutch at 9k miles.
To say he was rough on clutches is an understatement.