Admin System Lag 3.5.2 update

Greetings, I’m having a pretty serious issue after updating to 3.5.2 with sub-domain multisite enabled.
My network has 12 active sites on it and performs decent with 3.5.1.
Admin dashboards load from 4-6 seconds. When I upgrade the system to 3.5.2 it does the wp-admin/ request and lags there for an average of 2 minutes!
The public side of things isn’t really affected, maybe a few milliseconds.
Has anybody come across this issue after updating?
It’s acting almost like a process is hanging. :-/ And no new/different error are being logged in the debug.log file.

FYI: I’ve restored back to 3.5.1 and currently migrating to development server for further testing.

Thanks,
Vince