Shock oil

Assuming that the shocks are OK, they shouldn't rebound quickly enough to cause the truck to "bounce." It is likely that the chassis slapping the ground is what is causing it to come up off of the floor. If you don't want the chassis slapping, go with some heavier shock oil; but if you do that it's going to affect the handling on rough terrain. Suspension setups usually involve some sort of trade off.

Aside from just dropping the truck on the ground, you really need to see how it behaves while you are running it.