The PCM tells it when to shift and when not to. I uses inputs from various sensors to determine the shift points. You'll need a scanner that allows you to view the current data and look at temp sensors, etc. Also, check for DTC's(trouble codes). This may also lead you in the right direction. Good luck. Repost with more info and I'll keep trying to help ya.
Saturday, December 20th, 2008 AT 1:51 PM