Ford Repair: f250 5.8 racing engine, throttle position sensor, vacuum leaks

Question
My engine started out going to high idle towards the end of the summer. Progressively it has gotten worse. I have removed theintake hoses and cleaned the throttle body as far back as i could go. I made sure the buttewrflies were closing all the way. Checked for vacuum leaks and replaced a few hoses that were questionable. I pulled the IAC valve off and replaced with a new one. I unplugged the battery and let sit for 30 minutes to reset the computer. There are no codes or check engine light. I don't have a tach hooked up but it revs and holds at around 1500 to 2000 rpm.  Any help or advice on which path to follow woould be greatly appreciated.
The truck is a 1991 F-250hd  With a 351 5spd 4x4

Answer
It sounds like you are on the right track.  If you are sure that the throttle body is closing completely, and not being held open by the throttle position sensor; I would continue checking for a vacuum leak.  You may have an intake manifold leak, or a leak in the brake booster, check valve, or supply hose.  A trouble code would only be set if a sensor is out of it's normal operating range.  A sensor can fail or stick, and still read normal to the processor.

I hope this helps,
Dave