I have 2004 GT and want to do these upgrades and want to know if I need to do anything else to add the following
3.73 gears
SR Performance Coil packsSR Performance 70mm throttle bodySR Performance throttle body upper intake plenumBBK 1 5/8 inch tuned length shorty headers ceramic
MBRP installer series cat back exhust

 

Well you're going to want to get a handheld tuning device to correct the speedometer, and you can save yourself quite a few bucks by skipping the shorty headers.....they will add little to no hp gains. Longtube headers or dont bother. IF you go longtubes then you will need to get a custom tune to avoid an engine light and get the most out of it