I have the same problem (see thread here)
The first time I docked post-upgrade I go one monitor. After a reboot I got no monitors.
In the Screen resolution dialog no monitors are detected, and if I WIN+P to 'Extend' it just sits doing nothing.
Joe, do you have any luck plugging your miniDP cable straight into the SP3 instead of the dock? (I didn't, but it's worth a try).
I've been out of town a few days, so haven't had a chance to try other drivers...
Edit: Note mine is the HD4400 on I5