If you need to travel down a hill, you should switch into a lower gear:

Question

Always downshift before beginning to drive downhill. Forcing an automatic transmission into a lower gear at a high speed could damage the transmission and also lead to a loss of ability to engine brake. Drive at a speed that will allow you to control your vehicle without overusing your brakes. When determining a safe speed to drive, you should take into account the steepness of the grade, the length of the grade, the weight of your vehicle, road conditions, and weather conditions.

Accepted Answer

Before you start moving downhill.

Answer

After you start moving downhill.

Answer

As you go downhill and pick up speed.

Answer

Near the bottom of the hill.