In most GM vehicles it's just to the side of the glove box. You'll need to pull the glove box apart to get to it. Usually it's just a few screws.
no
... what about them?
NO IT WILL NOT WORK. The 99 MUST HAVE A 4L60E TRANSMISSION put back in it.
Yes
No, gear ratios are different.
autozone website i got mine off of there for a 91 camaro
Around 1-3 MPG less in both city/hwy
Check
whats wrong with it?
305 or a v6
Yes
You can not. If you are experiencing a particular problem you can check TSB's for an updated PROM. That is Program Read Only Memory. It would have to purchased through the dealer.