i would have a look at the firmware version on the ssd you have and also have a look at your bios version, you mention that your old setup had similar problems, were you using the 980 pro ssd back then?.
Kinda a long shot but it could be a faulty ssd, when the 980's first came out there were reports of laggy/stuttering behaviour in windows and games and it was found to be a faulty batch of ssd's from samsung were to blame, a firmare upadate was released and it was highly recommended to install asap, the drives that were affected were the 2tb versions but lower capacity were also impacted, if your drive has firmare verison 3B2QGXA7, you need to update, download a program called samasung magician, within in this program you can check firmare versions and update if outdated.