When to change suspension springs

How do I know when my suspension springs are done? I drive a 2006 Dodge Ram SLT Quad Cab 4WD.

Unless they’re broken or sagging there’s no reason to even think about changing them.
A factory manual (or a bit of free info from a dealer service writer) can provide a ride heigh specification.

Check your vehicle against that spec. On an '06 I doubt there’s a problem.

My 1972 W-250 Power-Wagon, with thousands of miles on washboarded dirt roads, is still suspended on it’s original springs… If you must change something, replace the shocks…

Why are you asking the question? The answer to that will help us answer your real question.

I think that the OP is confusing the truck’s springs with its shock absorbers.

As ok4450 stated, unless a spring is actually broken, or there is visible sag on one side of the vehicle, or unless the original ride height has decreased, springs are not replaced.

On the other hand, shock absorbers do get replaced when they are worn, and if this truck has been driven a lot on bad pavement, then it is possible that the shocks could need replacement after only 3 years of use. If the truck continues to bounce after hitting a bump or a pothole, or–much worse–if the front end “porpoises” up and down when driving at highway speeds, then the shocks are due for replacement. If in doubt, have your mechanic check them.