I recently bought a 93' C3500 dually and when I first brought it home it was running and driving fine not lately the truck doesnt want to go into overdrive. If I pull over and turn it off for about 5 mins and start going again it it fine until the first time it has to go out of overdrive then it will not go back in. I believe its a 4l80E, a mechanic told me it could be input or output speed sensors on the transmission or a transmission control solenoid. Anyone have similar issues?