sounds like an 02 sensor, or a tps- its going to to limp mode when you say it runs like a champ. probably 02, it wouldnt have any throttle response in limp if no tps function. bad 02 could be pulling down the signal or response that may or may not be some how connected to the Ac relay input (thats not there) on the ecm?
unplug the 02 sensor(s) force it to limp right away. if it does id start there.