Forgot, did you installed the NVidia drivers or relied on the MacOS ones?
You can fin them here:
https://www.nvidia.com/download/driv...px/93555/en-us
But you need to add a value in your Clover config.plist.
https://www.tonymacx86.com/threads/n...clover.202341/
In your case, it would be nvda_drv=1 as you're still running El Capitan. Worth a try...