have u ran a diagnostic test on it if not make sure that u use a really nice scanner cus for example I have a $400 scanner and it reads all the sensors that are controlled by the PCM and the trans has many so it should let u know if u have a bad sensor. cuz honestly, that's what it sounds like u have going on I have experienced this with a customer a while back. if u go to your local auto parts store they can run a test for u also keep in mind the dash lights don't always have to come on check engine wise. for there to be an issue I have run many tests with no light on and long behold trouble. hope this helps let men know how it goes good luck