K, given the mods in your signature i would say you're options are:
Obviously a cold air intake, But there are many arguments on whether or not that will actually help seeing how you have the
K&N already. For now you can remove the silencer on the airbox, it's a large funnel shaped rubber pipe going into the fenderwell, Just push the rubber around on the airbox side and it should pull out.
IF you were to get a cold air kit, Make sure it is one that has a rigid pipe from the filter to the intake plenum,
Intake plenum,
Gives you a few extra ponies to work with given you are able to pull air with less restriction and a percentage more volume. I personally like C&L plenums
Throttle Body,
This is one of the cases were bigger isn't always better, 70mm and 75mm are the most common, Beware though that more air coming in could lean out the engine!! if not properly configured in the Ecu.
Tuner
High priced but high efficiency, This pretty much opens up the door to any power adding mod you can do, and with a good person doing the work you gain power and the engine is working more efficiently - I:E, Better fuel economy I strongly recommend
http://www.bamachips.com/store/inde...h=18_8&zenid=a3707b98f94e2917c60b09f7e2783738 for tuning work, He is local to me and i have had tunes made from him on a couple different stangs with awesome results. Around town we call him the Wizard lol. Plus like several other companies, if you purchase a tuner from him you get free retunes every time you do another mod.
Exhaust,
Flow masters have opened the backside up a good bit but consider a mid pipe, H or X, you're choice there, sound is crucial to some people lol. Headers, PITA to install but not necessary unless you are planning on forced induction or big internal mods. But if you want a much louder car, By all means
Maintenance
Really does play a big part in performance, The vast majority of members here will tell you the same thing, Motorcraft plugs and filters continuously provide the best results, Do a search and see for your self. Quality fluid are vital, if you haven't already our engines can run very well with 5w30 over FoMoCo's labeled 5w20.
Forced induction,Nitrous,Heads&Cams open up a whole different story...
Read through some posts and see what members have listed in their signature lines and see the results they achieved, You might be surprised !!
Ask Away
Joey