I use Windows 10 on a laptop and recently (a month ago?) I had similar super-high "usage" issues (90+%). I ended up doing perhaps 10 different things (anti malware, anti-virus, defrag, etc. etc. multiple times and finally that problem seemed to resolve itself - but I have no idea IF anything I did fixed it or it "fixed itself" somehow or realGM fixed it.
In other words, PERHAPS, I'm adding my voice to yours over the same problem.
But maybe not at all - what the bleep do I know?