I recently purchased a 2004 mustang gt with 30000 miles. I am new to the mustang modification so here are my questions. I have a auto transmission, can I modify it or replace it with a better auto tran? What kind of engine mods can I do? What kind of gears will it take? What are good fuel additives can I use to clean the fuel system? Thank you for the help.

 

You can modify it yes, with a shift kit, you drill out the valve bodies to give much more firm shifts. You can also pick up a torque converter with a higher stall. I'm not totally read up on the autos, because my stang is a 5 speed, but I hope this helped.

Engine mods? Everything... but bolt-ons will not get you very far... you can beat full bolt-ons with a simple 125 shot of nitrous

I'm not sure on fuel additives, you shouldn't have to worry about it any time soon. When you do, you'll be better off having it done professionally (injectors cleaned individually etc).

If you want to learn the most, go to the 4.6 tech forum... more people visit there than general tech.