I believe the 2006 - 2007 Grand Prix GT became the "GTP" model. The 2006 - 2007 Grand Prix GT however did NOT always come supercharged. Most places bought these cars for "fleet" purposes and they are usually the GT's that came non-supercharged. So when looking for a supercharged Grand Prix, you really have to look at the engine. Or, even just driving the car you should be able to hear the whine of the supercharger. If you're not sure what you're looking for, you can always google what the supercharged engine looks like. =P
