Whats the best 04 GTP battery? I need to replace mine and dont know if i should go with AC Delco or other? Also what are the best Spark plugs NGK platinum or iridium or Bosch? how good are the MSD ignition coils? please reply. anyone know where i can get a decently priced PCM?

Your battery depends on if you live in a cold climate and so on. Iridium plugs are better than platinum but dont waste your money on coils cause the ones in your car are already very good and they rarely fail.

https://www.zzperformance.com/grand_prix/articles1.php?id=23

As for the PCM..I just installed one from zzp (along with a 3" catless downpipe) and it made a good difference in the driveability. I didnt need a case learn (I have an 04gt), just a key relearn which i did in 10 minutes easily.

here is the pcm...

https://www.zzperformance.com/grand_prix/products1.php?id=182&catid=107