I'm sorta shocked about this one. I was at the dealer getting something else repaired, and asked if there was anything they could do with the mirrors. The seem fine 'til I towed, then they just were annoyingly shaky and hard to see out of. I have those manual ones you pull out when you're towing; they have blinky turn signals and are power adjustable, and have extra convex parts on the bottom.

Anyway, I was expecting them to say they couldn't repro the problem -- but when I got my truck back, I got the following info:

TSB 06-08-64-027E Relearn Power Folding Mirrors for Vibration.

I haven't had a chance to check it out yet but thought I'd pass it on.