I've had this problem since the patch as well. I usually limit my framerate to 60 fps, and the game runs very smoothly like that. Since the patch the game has been dipping to around 40 fps many times a minute.

Things I tried:
Cleaning the fans of my computer
Checking all drivers (they are all up to date)
Changing settings in NVIDIA Control Panel
Overclocking the graphics card
Restarting the game
Restarting the computer
Shutting down other apps and programs (and game mode)
Switched between DirctX9 and DirectX11 at game startup (the problem persisted in both)
Changed fps way settings in the game between 15 fps to 120 fps (the fps still dropped/skipped many times per minute, whether the fps was high or low)
Changed the graphics settings from lowest to highest, and back to lowest

None of the above helped: Even at low settings, the fps will suddenly dip. This didn't happen before the patch. If I try to use skills or spells at the same time as the fps skip/dip, the action doesn't go through and I have to use the skill/spell again.