Free GPU driver cleaners can cause problems since they get revenue from tracking you.
Best to uninstall them and download the latest driver directly from nvidia.
Do a clean install.
You may want to do a custom install and omit such options as 3d, sound.
Perhaps even nvidia experience .
Do you have any sort of a temperature problem?
Run HWmonitor.
If you see a max temperature around 100c. then throttling is likely an issue.
If your minimum temperature is much above 10-15c. over ambient, you may have a cooler problem.
Have you overclocked your 8600K?