I have a 2000 intrepid 2.7 the voltage stays at 13.5-13.8 at all time sitting or at 80mph, if I give it enough gas to hit passing gear it spikes to 19v and drops as soon as it leaves passing gear, I have put it on a computer and no codes or troubles come up even when the spike is present???? before I cook the computer I would like to know what is causing it, I took it to dodge dealer and they said it could be a sensor in the transmition, any ideas???