If your going to do it do it right. Get a cold air intake with a tuner. They make more power period. The tuner can also read and clear engine codes and let you makes changes for bigger tires/wheels. For $550 you can get a JLT CAI and tuner that will give you better throttle response and firmer shifts in an automatic and add 20+rwhp.
2005 Ford Mustang GT Torch Red Manual
Saleen Super Shaker 3.4 pulley/Brenspeed Tune
Kooks Longtubes Catted H/FRPP Stingers
Full BMR And Steeda Suspension
SOLD!! I have no Mustang at this time!