I agree with the previous posts but if 4.2V at wot bothers you, there are a couple of things you can check. First, measure the voltage between the TPS grey wire and black wire (ground). It should be 5V and any less will reduce your wot reading. The 5V is supplied by the ecm (pin C14).
If the +5V is good, then make sure the throttle is actually full open. Have someone push down the gas pedal hard while you check the meter. The most common causes of low tps wot volts are the transmission tv cable preventing full wot and/or a floor mat is interfering with the gas pedal.