Since you have a nvidia card, go to nvidia system settings -> manage 3D settings -> Program Settings and select the eso64.exe.
Now just set the "Background Application Max Frame Rate" to something low like 10 or 20.
This should cap the fps to 20 whenever the game is not on focus and result in lower gpu usage.
Thank you for posting your solution to the 100% GPU loading. With the issue resolved and this thread now several months old, we are now closing out the discussion.