The M1025 Humvee will not accelerate after these conditions, until the engine is restarted.

1. Drive Humvee up a hill and let go of W, wait until Humvee comes to a stop then press W so it rolls backwards down the hill.
2. Drive Humvee up a hill and hit an object, causing it to stop and start rolling backwards.
3. Drive Humvee up a hill steep enough that it can't climb it and begins to roll backwards.