3.27's in all 2002 Supercharged Saleen Mustangs. It was an EPA thing where 3.55's were not supposed to be installed. It was an option but was not supposed to be done. The best way to know what you have in there is to get both rear wheels off the ground. Mark the driveshaft at the bottom with some chalk and count the turns. If you are not the original owner that's the only way to know. I know guys who think they have a certain gear based on the type of trans and RPM's at a certian MPH but lot's of SpeedCal's have been installed since it's the easiest way to correct the speedo without playing with the tune. Good luck!