I have a 2001 2wd f150 and after changing a drivers side flat in the rear my truck started shaking at low speeds and when coming to a stop. The check engine light came on and the overdrive light started flashing on and off. Took it to the dealer and diagnostic said it was an electrical malfunction inside the transmission. didn't fix it at the time and drove for about 3 months. fixed itself temporarily and then just now started the same thing. dealer found metal shaving on dipstick. what has happened and is my best bet to get a new transmission?