Why is my game lagging so randomly?

scanner found nothing to fix. ran the repair, no changes.
I use spybot S&D weekly, defrag/optimize weekly
vpn made no difference.

background apps running using anything listed as higher than medium impact:
Wow 21.3%cps 4,582 mb memory 69% gpu
opera GX - 0.2% cps 610mb of memory
literally everything else in process list is using less than 100mb of memory some as low as 1-2mb .(21 more items listed)
ran a memtest last night(6 hours worth) 100% passed
samsung magician reports zero issues with any of my drives

on an outside chance, WOW is NOT installed on C drive. though i doubt that would make any difference what so ever.