Quote Originally Posted by Scimmia View Post
HOLD ON A MINUTE!

The diff ratio is different, 3.05 in the Regal vs 3.29 in the GP GT. This means you would need to reprogram your computer, since I'm pretty sure you can't use a Regal computer in a Grand Prix (BCM issues, I believe). If the diff in your current trans is still in good shape, you could swap that in and you should be fine with your stock computer.
I thought GP BCMs were pretty accepting. It's the Chevy and Buick BCMs that give issues.