I just finished installing the SLP headers x-pipe, and catback on my 01gt. I received the catback about a week before the headers because they were on backorder, so i of course went ahead and installed the catback first. The change with the catback was very noticable. Throttle response was much better, alot quicker. The sound was very nice. Well the header installation was not as easy as I had hoped, but then againwe did not remove or move the k-member at all. I had to go to work and I had a buddy of mine wrap up the installation. He called me and the first thing he said was that my car now sounded like a NASCAR. I was like right whatever. Well when i started my car up i really did not notice anything. I reved it and it actually hurt my ears! Let me just say it is so much more fun to drive this car now. Below about 2200 rpm there really is no change....just a nice pleasing burble. Well go above that and it is a different story. People will deffinatly hear you coming. Everyone has nothing but great comments about what they hear and you always get the second looks. I would recommend this exhaust to anyone who loves the sound of a racecar on a sunday afternoon. I don't really care if these guys made products for GM in the past. The fact is they make a killer exhaust for my ride, it is a quality peice that went into the car nicely and I am very, very happy with the outcome. GO SLP!!!!!