I can get a really good deal on a Grand Prix that needs a trans. What could I get a trans out of? I have someone will a 94 impala ss trans, a 2000 impala trans would either of those fit?

Call a salvage yard and they can tell you .

1994 Impala SS transmission is not even close.
2000 Impala is closer

1997 was a transition year for the 4T6x transmission be careful what you buy.

Then: If you're buying used, you inherit whatever issues that it already had.

My suggestion: If you are going to keep the car for a while, and you don't want to spend a lot of time swapping transmissions into it, pay foe a rebuild at a reputable shop.

While we're here: What'* wrong with the current transmission?