I have an early 2013 27"iMac that I just updated to Yosemite. Not only is Safari lagging to the point that I had to install Chrome, but I can't seem to install my Mac updates in the App Store. The App Store comes up sporadically and with difficulty, let alone the"updates"window. The later concerns me more than anything. Is anyone else having this particular issue? Activity Monitor shows little CPU usage. The wifi it's not the issue either.