If you don't want anything special, just buy some Valvoline PSF. If you want something better, get some Redline PSF (not ATF). ATF might okay, many people have used it, but I have always used PSF in GM vehicles. These are the fluids I've used and they work good. The Redline works especially well if you have any cold weather issues. I just got rid of my '01 Grand Prix and I only ever used Valvoline PSF for 230,000 miles and never had an issue.