Windshield wiper "stutter" ...but not consistently.

[freeclimbmtb]

'03 GMC 2500HD, 6.0, 5spd, WT package.

 

 

Noticed it this morning while driving through this lovely nor'easter we've got going, the wipers function normally until they are vertical on the windshiled, then they just pause and skip for a second before finishing the last inch or so and reverse. The problem sort of came and went on the drive in today, didnt seem to matter if it was in intermittant, slow, or fast. One minute they would be bouncing around (always when the blades were at or close to vertical) then within a few minutes they would be working normally.

 

I found something like this about a trailblazer...but i think in that case it was limited to when the wipers were in intermittent mode..

 

Thoughts?