I have a 2003 2500hd GMC Sierra 4x4 with 6.0L and a 4L80E. Im having some quirky problems with the torque converter lock up. It will lock in and out continuously while pulling hills with a trailer. I've unplugged my brake controller and changed the brake switch. No change. I've always read that when you tap the brake it is suppose to unlock the converter but mine does not. Should I be able to tap the brake and unlock the converter? What other switches control that besides the brake switch?