If you run a 3.05 diff when the computer thinks you have a 3.29, it'll throw a code and max out the line pressures, it'll be shifting at the wrong times, your speedometer would be off, etc. Not a good idea. Either reuse your current diff, get another 3.29 diff, or reprogram your computer.
Sabrewings, I know for sure you can't use a GP PCM in a Buick, and I've always been told you can't go the other way, either. Even the gauge clusters in the Buicks get their signals differently than the GPs. Mechanically the cars are pretty similar, but electrically the Regals and the GPs have quite a few differences.
Originally Posted by Scimmia
