If I was gonna get a 04 GTP this is how I would mod it in order.

Cold Air Intake.
Complete exhaust headers included.
Rockers 1.9 Intense.
PCM with programming for the rockers.
Intercooler from intense w/spacers and injectors.
SLP MAF w/ adapter and supportive programming in PCM.
Colder plugs and Modular pulley system.

Really the last three would be done mostly together. But with a 3.4 Intense Dyno shows about 280 horse. Just on the virge of blowing the tranny. And with the smaller pulleys you probably would.

Purpose of post = Nothing.