Based off the information you have provided, I would like to ask a few questions to see what has been remedied to try to address the issue.
1) Have you updated your addons recently with Curse Client?
Sometimes when these addons are not updated or are no longer working, believe it or not, they can cause disconnections in the game.
To test this, once you log in, click on the AddOns button and attempt to disable them. After they are disabled try to play the game for as long as you can to see if it will disconnect.
2) What type of internet connection are you using?
Wireless connections are normally not supported as they are unstable and can cause disconnections as well.
3) Have you considered trying to update your Network Card?
Sometimes out of date network card drivers can also cause the game to crash as well.