car feel different after header install. or maybe im tripping.

Listen, A GEN V is a more efficient blower which means you can use a larger pulley for the same amount of boost than you would need for a GEN 3. This means..

3.4" GEN 3 = 3.6" GEN 5

- Rule of thumb is .2" .

As for the guy who said you need to upgrade your spark plug wires, he is wrong, the stock ones are excellent and if you do have to replace them ( tune-up, high mileage, etc ) just buy factory ones unless of course you want colored ones.

Headers lessen the back pressure... so yes it will not feel as torquey BUT you will have better top end and that is where our cars suffer. If you want to regain torque then you are going to need to drop pulley sizes. I see you have an 04+ so I would go with a 3.6 and get it tuned. Did I mention get it tuned? If anything at LEAST get it scanned for KR, you don't want to blow anything up. Tstat/plugs help but it really just masks KR problems. I would go with an intake, headers, 3inch DP and some tuning to run the 3.6 along with other small supporting mods but those are the major ones. If you really want to be safe throw on some rockers but if you plan on modding more in the future just skip straight to a cam. As far as the catback goes there is no need to replace it until you are hitting 12's in the quarter mile.