07 GP GXP here as well. Bought it in '10 with 5k miles. Now has about 55k. I mostly use it as a daily driver. Only 'mods' are the k&n intake box and a DMH cutout right after the cat. I've got a boosted ls3 vette and a l67 swapped / whipple charged monte carlo, so I haven't really had much desire to mod the GP.

Ran 14.0 @ 100 mph the one time I took it to the track.