Originally Posted by Hoese37

What youre getting is called chassis slap. When going over a jump your suspension is soft to the point that it cant react quick enough and the chassis bottoms out on the jump face. This causes it to buck up in the air. This can be fixed by going up in shock oil, and/or changing pistons.

When changing pistons you are adjusting the pressure inside the shocks. This is referred to as "pack". The pistons can only pass through the oil as quickly as the oil can flow though the holes. I it can pass to easily, the shocks wont support the weight of the truck. A piston with more pack will create more pressure. The faster the shock packs up, the firmer it becomes.