As said, stock are the best. Check with advanced auto, I know they car order them.
Have you read ZZP tech articles? Make sure you read the mods you don't need writeup.
https://www.zzperformance.com/grand_prix/articles.php
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03 GT, STB, GM HD sway bars, 35% tint, GE893(37watt)fogs, Flowtech Terminators, 180 T-stat, ZZP DP & PCM, Ceramic PLOG & Crossover, 18" glasspack, 2007 17" Mustang Bullits 235/55/17 Pirelli PZero Nero, 12" R1 D\S rotors, gutted air box, GTP radiator