For a quick fix, (now in it's third year) I set the mirror angle to a good view, and then put a half inch blob of clear RTV joining each corner of the mirror to the mirror housing.
No more shaking, and as a bonus, the RTV stays flexible enough that the mirror view is still adjustable using the inside the cab controls.
Some day I might take it apart and fix whatever is wrong with the plastic supports that live behind the mirror glass...or maybe not.....but if I do the RTV will just peel off.
rScotty