There's a sneaky trick that improves the performance of vacuum wipers- - - - -put a big vacuum reservoir on the truck, one that stabilizes the operation of the wipers when the vacuum drops momentarily. A long piece of 2" PCV pipe with caps glued on both ends bracketed inside a frame rail, with a one-way check valve between the intake manifold and the reservoir will allow the wipers to operate for several seconds with low manifold vacuum. As soon as the hill levels out or you complete your passing maneuver, the vacuum refills the reservoir "tank". Paint the pipe black, and it virtually disappears inside the fame.
Jerry
