The BEST throttle body is the Accufab... but its a rip off for the price they want. The one to get, as has already been stated, is the Trick flow 75mm TB/Plenum combo off of Summit. Just changing the TB is a waste since the plenum on the 99-04 cars remained the same from 96-98 and is restrictive. Going to a bigger plenum along with the TB will open things up like they should be.
2000 Mustang GT Steeda build #48. Bolt ons, suspension, Novi 2000.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.