Use Low Gear in A/T.
Its mainly used when you need engine braking or more power. so if your towing or have a heavy load going up a hill, if you shift down your engine's RPMs will go up and you will have more power. Also when going down a hill when towing or with a heavy load, the engine's RPMs will go up. So if you leave your foot off the gas when rpms are high and going down a hill, you will have engine braking. this means that the engine will slow down the car because its at high rpms but your not giving it gas, so it naturaly slows down.