Directly from the repair manual:
"3 Before checking the throttle position sensor, check the voltage supply and ground circuits from the PCM. Disconnect the electrical connector from the TPS. On all except 4.7L V8 models, connect the positive lead of a voltmeter to terminal number three and the negative lead to terminal number one of the harness connector... Turn the ignition key On - the voltage should read approximately 5.0 volts. If the voltage is incorrect, check the wiring from the TPS to the PCM. If the circuits are good, have the PCM checked at a dealer service department or other properly equipped repair facility."
Myself not being a master repair technician, I followed the above instructions and got a reading of 1.8 volts. This just so happens to coincide with the P0122 code - TPS voltage low. So, again not being a master repair technician, my thought is "crap in, crap out". If it's low before getting to the TPS, I'm led down the path it's not the TPS. And this is where I'm at now.