I'm gonna take it your truck has a Cummins B or C series engine. Yes, you have to REALLY tighten the linkage down on the Bosch injection pump. I think when it gets loose and stays that way for a while the shaft will have a groove worn into it. You can pull the arm out about 1/8 of an inch and tighten the link down again, using a 10mm socket and backup wrench. Replace the throttle return spring (Its made to use two, but two will make your leg hurt so just put one on, and keep spares) And re-align the throttle cable bracket. And if the link remains tight when checked on occasion, this will save you from an injection pump rebuild.
-Weave- From mirrors to stupid engines I THINK I've just about broke everything!