Like John says, the shock absorbers are the first thing to check. They are there to damp vibrations (i.e the bounce). Check for dents in the outer tube and any signs of oil leakage - usually fairly obvious when they need to be replaced.
Not a big job to replace them.
Any truck will tend to bounce when empty - afterall they are designed to be laden and earning their keep carrying goods/materials etc!
JD, April 2008
