Leader, if I remember right the TPS voltage goes from about .8VDC to around 4.7VDC. To test the component remove it and test with an ANALOG Ohm meter. Connect the meter accross the wiper and one end of the Variable Resistor) VR. Then turn the VR slowly so you see a decrease or increase in the Ohm value (depending on how you hooked it up).
Turn slowly so if you see the needle Jump and can reconfirm by backing up over the same spot and doing it again... the TPS is bad. There's a bad spot in the VR. You're looking for a smooth transistion from low to high Ohms. Rapid needle fluction means you've come over a dirty spot in the TPS.
Once you've confirmed the TPS is good, look elsewhere. The voltage you quote does seem low, however if the voltage is 30% low at WOT, that's more than enough for the computer to signal a TPS code.
From the description the problem seems more akin to the following:
MAP/MAF sensor: Monitors Engine Load.
IAC motor: Controls Lean/Rich at idle, and can lean an engine out too much, even under load.
Fuel Regulator: Failing to deliver enough pressure under load to the fuel rail/injectors. This is confirmed by a pressure gauge on the schrader valve.