Have you checked the IAA/IACV? If I remember correctly the IAA/IACV should not effect the engine above a certain RPM. Only at lower rpm range. Have you checked for vacuum leaks? If you could determine lean or rich when the engine stumbles might help point you in the right direction. If you just disconnect the wire going to the IACV the engine should run at lower idle, but if you still go through the motions to cause the engine to stumble and it still does you could probably rule out the IACV. My car was doing something very similar and turned out to be TPS like you mentioned. Seemed to read okay on voltmeter but when going from WOT to idle would throw it all out of whack. Hope this helps.
