The TPS isn't available from Ford separately. You would have to purchase a $125 throttle pedal assembly. The upside of that is the pedal is extremely easy to replace, the downside is the cost trying to fix an unknown problem.

Somewhere up in the diesel forums is a link containing information on how to get a TPS without the rest of the assembly. I'll look for it this evening.

Does the Bully Dog tuner have any diagnostic capabilities besides reading codes? If it does you can pull up the input voltage to the pedal and watch it to see if it falls off when the truck acts up.

How often does it act up like this?