A shudder is almost always blade or arm related, either the blades are shot, the arms are twisted, or the connection between the blades and the arms is too loose. Put new wiper blades on the truck, its the cheapest place to start and the most likely problem. They tend to "lay over" after they have been against a windshield for a while. When the wipers are running, the blades shift from side to side as they go across the windshield. Old, laid over, blades don't shift over very well, and tend to shudder. Also check to be sure the blades are not sloppy loose at the pivot points where the blades attach to the arms, as that will also cause a shudder. Gene