I also have a 04 Grand Prix GT. I have a K&N air intake and a high flow exhaust on my car. I installed the PCM sold by pfyc.com that is done by Digital Horsepower. I didn't have to do a case learn, only the security lean and there are step by step instructions that come with the unit. It is a great product! More power, better throttle response, and my K&N even sounds better.