The A #1 most important variable affecting ride quality is shock absorbers. Cheap one-size-fits-all twin-tube shocks are almost always the culprit. As an aside, the next biggest factors are tires and suspension bushings. Springs are in a distant forth place if they are sagging or broken. Control arms have no impact on ride quality.
Back to shocks:
-- Great shocks cost more (under $200 per corner), but for what you get, they don't break the bank. Once installed, they will likely transform your driving experience from garbage truck to modern luxury car. Our shocks have a 1,000,001 mile warranty.
In contrast, some of the El Cheapo twin-tube shocks start out bad and get worse. By "start out bad", I mean that you get a generic calibration that feels sloppy and/or harsh. The one-size-fits-all shocks are prone to bottoming out. You can easily inspect your shocks to see if they are crashing into themselves. Also, attach cable ties to the shafts, go for ride and see how much they move.
By "Get Worse" I mean that many gas charged twin tube shocks utilize plastic gas bags that quickly fail which allows the gas to escape resulting in horrible ride quality.
Before you go changing everything:
-- Inspect the dates on your tires, ancient tires will hurt ride quality.
How old are your tires?
-- Inspect your suspension bushings with a flashlight. Poly bushings yield a harsh ride. Same for worn out rubber bushings.
What bushings do you have?
-- Inspect your springs with a flashlight to make sure they are not broken or sagging.
While you are under your truck, note that shock absorbers are the easiest parts to change in the whole system, so start there. Before you go changing anything else, upgrade your shocks. We've been through this a million times. The merits of really good shocks -- in terms of driving experience -- far outweigh their higher cost. Everyone raves about our shocks for good reason.
http://www.ridetech.com/products/q-series-shocks/
Thanks,
Steve