Long load times and dramatic FPS drop. At a loss, need advise

Hello all,
The other day while playing Assassins creed Odyssey, The game took much longer to load. From 30 seconds in the past, to four minutes. My FPS during that session averaged between 11 and 17. They used to be in the high 60s. I've also noticed the computer is a bit slower while opening browsers, spreadsheets, etc.

I've pulled the drive and replaced it with a mirror image (same exact drive model) I created 3 months ago. Same problems. I've swapped power supplies, same problems. I've run a plethora of diagnostics, and everything seems normal. I've tried different drivers. I'm current now, but I've also rolled them back. All Processor cores are stable and maintain normal operating temperatures. RAM diagnostics reflect no issues. PSU voltages are normal. I initially omitted the GPU because of the load times, and overall system punchiness during non-game tasks. Maybe I shouldn't? I didn't think the GPU would affect load times so dramatically. I'm desperately seeking suggestions.

thanks

Despite this clearly appears to be a desktop still check to see if somehow it was set to "Power Saving" mode plan for any reason in "Power Options" .

Another thing is to revise in Nvidia's Control Panel > Manage 3D settings > Assassin's Creed Odyssey : that you selected "Prefer Maximum Performance" in "Power management mode" > Apply .

Also check and see if windows decided to update your graphics driver to some faulty version that hinders performance . Do note that if you are running an Nvidia GPU each released driver come to boost performance of certain games at the cost of hindering performance of others and they are constantly released to cover new releases of games (hence why they call them Game Ready drivers) so the Assassin's Creed Odyssey game ready driver was "GeForce Game Ready 411.63 WHQL" so check to see if you are on that since there had been not less than 5 releases after .

P.S You might want to set System > System Properties > Hardware > Device Installation Settings > No for as long as you are playing that game since Windows sometime have this nasty habit of re upgrading to latest driver a minute after you do the downgrade .

Thanks for all the help and suggestions guys!

Just an update

It's back to normal. I did nothing else than what I mentioned in my initial post.. It did this a year ago for a few days. It's troubling that I can't isolate the issue.
If I ever do find out, I'll post the solution so others will have it as a reference.