I was driving at 62 MPH and the truck suddenly down shifted. It is a 6 speed transmission and I was in 6th gear when it down shifted. The indicator that displays what gear it is in disappeared but the rpm went form 1,500 up to 3,000 very abruptly. In fact, when it happened, the back wheels actually hoped up and down a couple of times. I tried to shift in manually but nothing. I stopped the car, restarted and it would not upshift. I put the car into neutral while I was rolling and then put it back into gear and the transmission stared to act normal.