I upgraded from 2.61 I believe to 2.7.1. My host uses IIS I think. Never had any problems until the upgrade. Now Admin is painfully slow, even times out. When it does load, it's like only half the page is present and I can't edit posts or mess with plugins. I have seen some of the other threads. But don't see a definitive solution.
The site itself runs fine. I just can't administer it.