FPS problem on certain toons/locations

[Anyankha]

Hello, I've been having this problem basically since ICC times. MY FPS would drop to the ground in certain places and certain toons. My main (mage) doesn't experience this problem at all. On the other hand my shaman, and most importantly, my warrior seem to experience this. Some examples:

ZA/ZG: I can run these 2 smoothly on my mage, with an avg FPS of 50-60. Now, when I try to run these on my warrior, the moment I zone in my FPS drop to like 9-10 -if I'm running, or mid-fight it drops to 4- and the char's movement become very choppy, making it unbearable to play and affecting my performance.

H Sethekk, H MGT: Same problem as above. My mage can run those 2 places smoothly, but my shaman and warrior suffer the FPS and choppiness issue.

When it comes to normal heroics (aka, 85 heroics except zandalaris) my warrior doesn't experience the FPS issue (I don't play my shaman much, except for vanilla, BC and wotlk content).

I used the same addons for all my toons. The only difference is mage has combustion helper and the other 2 don't, so other than that, same addons. I redid ALL my addons a cpl times to see if that could fix it. Nada. I updated video drivers and nada. I ran out of ideas on what could be causing this.

Any help would be much appreciated.