Whoa Whoa Whoa!
Sorry to jump on you; I have NO IDEA where you got this info, but it's completely wrong. In 2004 the GT1 and the GT2 had a 3.8 N/A engine, and the GTP had a 3.8 S/C engine. All had dual exhaust.
In 2005 the Sedan (no letter designation) and the GT have the 3.8 N/A and the GTP has the 3.8 S/C. The 2005 Sedan is the one that has the single exhaust.
Actually, for a single exhaust I think it looks pretty good, much better than the vacuum cleaners on the other models.
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2005 bleen Comp G!
Just checkin' in periodically :-D