I just started having the same problem about 2 days too. I’m searching for a reason. I have read other posts in my search so far that W3 Total Cache could be caching pages, but that has to do with once the page is published and it takes a while for the change to appear on the website.
My problem is like yours… I go to edit a page or post, hit the Publish/Update button and it takes about 90 seconds or more before it saves the page. It almost locks up, meaning you cant even click another link in the admin area.
Ok… I just figured out my problem. It was one of my plugins. I basically went in and disabled most of my plugins and the problem went away!
So I started turning them on a few at a time until I finally found the culprit. You might try doing the same thing.
