[Stocker]

That's very close to what I measured mine at several years ago. Copied from my post back in 2012:
The 'button' that the mirror attaches to (my mirror is removed) is 2 7/8" down from the molding (to the top of the button; a bit over 4" to the bottom of the button).

Disclaimer: The windshield has been replaced once in the years that I have owned the truck. My glass guy is a real stickler for detail, so the button is probably in about the same location as before.