Sheesh I took long enough to get back to this - but for the sake of future generations I wanted to post how I fixed the problem.

It was indeed the linkage. Couldn't find a new linkage for sale anywhere so I took my chances on one I pulled from a wrecked Trooper in a junkyard. Works fine so far.

To replace it, you've got to:
-remove the wipers
-remove the large nuts on the wiper posts so the splined center posts fall down into the cowl.
-open the two small access holes in the cowl/firewall(each slightly smaller than the arms that have to go into them...careful they can be sharp)
-pry the linkage off the ball connector on the wiper motor
-lube up the new unit (I used lithium grease because it looks like what was already on there)
-install in reverse order. The snapping off/on of the ball/joint connector is the toughest part but not too bad.
-adjust your wipers on the splines so they sweep properly
-enjoy