The shocks are suppose to dampen and stop the oscillation of the springs. Without shocks, when the truck hits a bump it'll keep bouncing for a while. You can do a simple bounce test for your shocks. Push down on each corner of your truck, once it reaches bottom let go. The truck should come up and maybe bounce just once. If it keeps bouncing up and down, then you need new shocks. Like those cars that go down the road and hit a bump and then it continues to bounce up and down for many more blocks/miles, those cars are in need of new shocks.