What is the proper gear selection rule before descending a long, steep mountain pass (such as Salang Pass) in a heavy loaded truck?

1. Shift into a low gear that allows the engine compression to control speed before starting down the incline; never change to a higher gear or coast
2. Stay in top high gear to keep engine RPM low
3. Place the transmission into neutral and rely on the foot brakes
4. Turn off the engine ignition key to save fuel