I feel you dude. I am also on Zul’jin and I found FPS issues. But, I have found a slight fix to my problems. If you use addons, here is what you do:
Find your WTF/Cache/Interface folders and Cut or Copy/Paste them somewhere else (like desktop or something. Just make sure you delete the folders out of Wow. Then run Wow. This will force it to default, run like new, and recreate the folders again in wow. YES I KNOW THIS IS PRETTY STANDARD, but I am not done yet.
Check your framerate in game by hovering over you menu Icon. Also check your setting in advance tab to make sure your max FPS setting are maxed at 60fps (you can also do 30fps for lesser comps). If you are holding at least 30-50fps per seconds then you have a corrupted addon file, One you may not even be using any more. And this is how you fix it.
Go back to those old files you moved and find the Account/(AccountName)/SavedVariables folder in the WTF folder, also do that for the newly made folders too. This is where it can be a process if you want to keep your settings before you moved the folders.
Start with the addons you use the most. each time you reinstall a fresh copy of the addon, run wow. This will force it to make a new savedvariable file. Just exit out and look at the two folders. Copy/paste the old one on the new one if you want to get your saved profile setting back. Don’t worry about the .bak files. (in this process I found files of programs I haven’t used in years.)
Each time you log back in, check your FPS (let it sit and balance before you log out.) I know this sounds daunting but I didn’t do it all in one shot either. Take you time with it. Once done you Fps should hold steady better.
The Reason Why:
When you start wow it will try to load all addons and variables even though in game they are disabled, so if they are broken it will still effect the system. I went from barely holding 12-24fps in Great Seal to holding a good 30-50fps.
If that isn’t the case, go to Speedtest dot net and check your connection speeds.
If you do this and it doesn’t work, check your system settings and compare it to the Recommended System Requirements online. you might need to upgrade something.
If all of this doesn’t work then it might be either server side or time to buy a new computer (but that would be a very last resort).
I run a Alienware Aurora R3 with dual Raedon HD cards and I still get drops in raids after doing this but not as much, and dungeons run much smoother. It even runs smooth in PVP content. Like I said, a slight fix but it’s worth it to me.