Gmail slow sync across all Mac/Apple devices (not specific to Mavericks)
I've been experiencing gmail sync issuessince around 12/29/13. Google hosts my business email account, and it has been very slow to sync via Apple Mail on my MacBook Pro (OS Mountain Lion 10.8.5) and MacBook Air (OS Mavericks). I also downloaded Postbox, and that, too, is also slow to sync. Both my iPhone and iPad are slow as well. (By slow, I mean several minutes to download a message.) Access directly on gmail via a browser is instant and flawless. Also to note, my other gmail accounts (which are considerably smaller in terms of messages saved) have no sync problems whatsover.
The hosted account (which is experiencing all the sync issues) has more than 25,000 messages archived. I need these messages for my business, so cannot delete nor archive offline since they need to be accessed on multiple devices. Any advice on how to fix this problem is much appreciated. (Of course, Google offers no help whatsoever.)
MacBook Pro, OS X Mountain Lion (10.8.2)