throwout bearing, I had to have 4 put in my 01 V6... and it still did it
I would recommend doing a clutch, resurface/new flywheel, piliot bearing, pivot ball stud, fork arm, basically all of it and then check the end play on the input shaft of the trans to ensure its good.
Gonna have to take the trans out, may as well get your moneys worth
also look into an Heavy Duty Ford racing throwout bearing
DO NOT GO WITH ANY OTHER BRAND THROWOUT BEARING stay FORD