Sprags were all swapped out because, like many things, they are easily broken if you treat them wrong. Unfortunately sometimes wrong treatment doesn't seem all that wrong.
Your sprag needs one thing from you without fail: never let the truck move in a direction the shift lever says it shouldn't. For instance, if you are in a forward gear, don't let the truck roll backwards. And if you are in reverse, don't let the truck roll forward. And yes, that means that when you stop on a hill, you must not let the truck drift back while you get your clutch engaged.
Other than that, they need periodic adjustment, and the occasional repair from when someone didn't follow the above rules.
-Chuck