When driving down a long, steep hill in a truck with a manual transmission, which gear is typically appropriate?

When driving down a long, steep hill in a truck with a manual transmission, using a lower gear than the one used while climbing is the appropriate choice because it helps to control the speed of the vehicle. This technique is known as engine braking, which allows the engine to slow down the truck using compression rather than relying solely on the brakes. By selecting a lower gear, the driver engages the engine's resistance, which helps maintain a safe speed and reduces the risk of brake overheating, a situation that can lead to brake failure.

Using a higher gear or the same gear used for climbing could result in excessive speed and reduced control, while using neutral eliminates the engine's ability to provide braking assistance altogether, which is unsafe and inefficient in such situations.