have an 02 frontier with 3.3 V6 engine. replaced valve cover and intake manifold gaskets and spark plugs. truck shifts from 1st to 2nd gear fine and right before it should shift into 3rd gear the rpms go up and it does not shift. never had a transmission problem before. throttle position sensor threw check engine code. i tested it and all the electrical voltage tests came back where it should be. i checked all the electrical conections and evertyhing is good. if the sensor is reading the correct voltage but the light is on should i replace it or is there anyting else it could be?