Cool GTXWindows set to let other people get W10 updates through your PC ... Kill that
Cool GTXrun a security scan .... something is running in the background & if it is not visible In Task Manager ... that usually is Not a good indicator Windows set to let other people get W10 updates through your PC ... Kill that ---> does it happen when you are Not on a network / internet ? .... pull the cable / kill WiFi Indexing can eat resources W10 updates in background ? BIOS up to date ? What happens in safe mode ? I run a X99 Classy also
SajinTest each stick of ram individually with memtest86. You said you did deep tests on your ram... with what software?