What is a Cal Pac? I know it is a chip of sorts in the ECM and has something to do with either the transmission or differential gears; however, that is where my knowledge ends. I am the original owner of a 1989 GTA. Recently I had a new GM 5.0 litre engine installed to replace the woren out 5.0 litre engine. At that time I had a cam, headers and improved exhaust system installed. With lots of help from the TPI board I have defined the next stage to port the plenum, AFPR and new fuel injectors. From there I will move to the transmission and differential. However, if I start changing gears in these parts does it affect the Cal Pac? I did a search of this site but could find no information. Thanks for any information.