When you said wiper arms did you mean the arms that go between the pivots and the blades? If so then I would take a look at the linkage from the motor/transmission to the pivots and the pivots them selves. If you have too much slop at the pivots or in the linkage it is possible that one or both wiper arms go to far and bind. I am not as adept to the linkage setup on your truck but it seems that if you have replaced both ends of the system and it still locks up then the middle is all that is left.
I didn't do it, no one saw me do it, you can't prove anything! "Bart Simpson"
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