The vacuum motor was designed to move the original style low tension arms and thin wiper blades.A good vacuum motor will do ok with that at the speeds the truck was made for ,like 50 mph tops.With the stock 4.11 gears at lower speeds the engine needs little throttle,high vacuum, to climb slight grades, so the stock set will work ok.But once you put in hiway gears,go faster with more throttle depression,the vacuum wipers are fairly useless, slap themselves to death or are stopped dead.
