The manufacturers of shocks recommend replacing the shocks after 50,000 to 60,000 miles so some people do replace shocks as often as 50,000 to 60,000 miles which is okay and sometimes needed.
But I never replace my shocks until around 100,000 to 150,000 miles depending on how bad the roads I drive on are.
Sometimes the shocks get worn out too soon and need replaced but never before 100,000 miles because shocks really should last a pretty long time.
If your ride is becoming rough or the vehicle bounces up and down too much then it's usually time to replace the shocks.
If it's pretty easy to push down on the trucks rear end and bounce it by hand or by standing on it then your shocks on the truck are likely worn out and need replaced.