I know that this is an old thread but I am now experiencing the same increasing lag issue. I have played for hours before with no issues.
The game will play for less than a minute with no issues then gradually increase in lag until it becomes unplayable. Even attempting to logout our quit via the main menu will not register, need to "/quit" to close the client.
I have attempted the same uninstall/reinstall as above and it played for about 5 minutes before the increasing lag developed again.
If anyone has any thoughts, would be very helpful!