change the speakers too, the stock ones suck at best. and they are 9 years old now.

i just changed mine, and added a sub and amp. to the stock head unit, the difference is night and day, the radio is twice as loud with out the sub hooked up. just from the new speakers.

did you also get the harness to retain the steering wheel controls? it keeps the the door chimes and stuff working. i dont have a GP i drive a regal, but have heard of the dic not working right with a after market radio.

maybe someone will chime in on that if it affects your year or not.