Got this 01 2500 5.9 Mag. 4x4, having a heck of a time with the O/D off light. Start the engine, light comes on and stays on till you press button on shifter. Fan switch has to be on 2nd notch so compressor doesn't cycle. If you switch AC on while running O/D light comes on , it also downshifts if you are at highway speed, if you press brake pedal at highway speed , light comes on and downshifts. Have cleaned all grounds, replaced brake switch, replaced tps... what to do ?