I am having the same problem but have now managed to get my characters out of LA by guessing on another sever, the game runs fine until i then go near some form of combat and then i completely lag out, whether its the frostgorge cham train or a wvw zerg. Its really starting to be annoying now as the game is unplayable.
And the funny part is that i am also with BT and it only started after the patch, seems odd to me.