2001 Ram 4X4. Today I was driving down I-10 at 75ish MPH and my truck suddenly downshifted. It obviously grasped my attention, and as I scanned my dash cluster the "O/D OFF" indicator light caught my attention. Once I got off the interstate (just a few more miles) I pulled into a gas station to put the truck into neutral and park, pressing the "O/D" button attempting to make it go away...no success. Anyone have any idea what would cause such a thing???