Comment by nikoftime

What's great is that after the update, it's already working better for me. For what it's worth, when I called Apple about it, both support techs I spoke to had experienced the issues as well. It seemed to be correlated with large inboxes and whether "All Mail" was enabled as an IMAP folder in Gmail's settings. It was generally recommended to not be enabled in 10.8 and lower, and is now recommended in 10.9+.