adding more hp in a 03 pontiac Grand prix se 3.1 liters

Sell it and buy a GTP. There are lots of nice ones around. I think you'll find performance options for a 3.1 are few and far between and the results are apt to be disappointing.

Agree with munron. You can improve the breathing on the 3.1 with a performance exhaust system and cold air induction. The two jobs will run you close to a grand however, and if you're lucky you'll see about 20 HP gain and a big drop in gas mileage for your efforts. Stay way from the Computer Chip swap, they won't do much, if anything.