The question is not clear whether you want to soften the ride off road, what jefe said, or stiffen up the whole setup.
Don't know if you even have a sway bar. I don't think they were stock on any 3rd gens. But icbw.
Little more i fro on what you're trying to accomplish would help.
Cheap n easy to stiffen up if that's what you're after.
Easy to reduce bounce or rebound to a degree with good shocks.
Other than unhooking sway bar if you have one, getting more suspension flex, you may need a (gasp) lesser spring rate to get that rear axle to move with the terrain and more independent from the rest of the truck.