I was wondering the same thing recently. I asked and got several different answers. I wanted to buy a used, reprogrammed PCM from a '98 GTP to use in my '02 GTP. Since some said it would work and some said it wouldn't, I decided to go ahead and try it. It works and works well.
I believe 1Hot97 is correct. A 98' PCM will not work, or work well anyway. The MAF settings are definatley going to be different. As well as a variety of other things. If it is apparently working, I would suggest a scan to see whats really happening.
A forum community dedicated to all General Motors makes and models owners and enthusiasts running the 3800 series engine. Come join the discussion about performance, modifications, classifieds, troubleshooting, builds, tunes, superchargers, maintenance, and more!