Welcome to my world since the most recent patch down load. Lag spike does not begin to describe what happens these days in all the new 5 mans and in BWD and BoT. I'm talking 30 sec to 1+ min spikes. Also, I get kicked to start up screen sometimes if I log off one toon and try to log onto another. I have guildies that get DC'd when they try to get back into BoT or BWD after a wipe (I'm not saying we wipe a lot )
The FPS decay I cured by not loading some misbehaving add-ons. Try not loading out of date add-ons that worked for me. I was going down to 7 fps (from 60fps) in BWD 2 weeks ago. Council was really, really fun to heal.