some people go without ever changing it. not a good idea. in the gm manual it says to check it around 90,000 to see if its low and add some. i just completely changed mine. it will cost around 20 bucks. you can either order the oil online or pick it up from a gm dealer. i got my gtp with the same amount of miles and just changed the fluid. peace of mind. this might help.

Pontiac Grand Prix GTP Eaton M90 Supercharger Oil Change Picture Illustrated Guide