I do, but I'm not sure, if you understood what I said.
Your computer has very good specs, so if it's still running slow after fresh installation and while CPU usage is at 1%, you must have some hardware issues.
I'd start with testing some components....
First of all...
Download
System Information for Windows (SIW
free version)
No installation required.
After it scans your computer, navigate to
Hardware>Sensors and post all info from there.