I upgraded to Mavericks two days ago, and I have found that just about every time I command-tab change programs, my computer freezes for about 10 to 30 seconds. I have done some Google searches, but the post are back from 2013. Is there something I need to do to stop the freezing? Looking at the Activity Monitor (which has changed a lot), I have this strange new program called kernel_task, and it is taking up 1.36 GB real memory. Is that suppose to happen? I think read somewhere that it should be taking up 200 to 300 MB. Is this causing the freezing? Is there a way to go back to Mountain Lion if these problem persist? Thanks.