I have an 07.5 6.7 with an automatic 6spd transmission. It came equipped with the tow-haul option. But not the overdrive on/off option. For in town driving I would prefer not to be in overdrive. Does anyone know if the overdrive on/off selection can be added after the fact......the dealership seems stumped. It seems like a straight forward question. Its just a additional option correct, like adding stock keyless entry or stock fog lights.