for a GTP, you definitely need to get rid of the U-bend. A u-bend delete or DP will give you definite results. If you do this go with turbo mufflers or a resonator with chambered mufflers. You need some baffling or the drone will drive you insane.
Exhaust is always subjective. What one likes, another will hate, that is why there are 100s of different setups, and everyone likes theirs the best. 80% of us hate the drone and rasp our cars give with straight exhaust. What your car sounds like inside is drastically different than what it sounds like behind.
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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