For anyone else still facing these issues, I realize I am bumping an older topic, however this was the only solution I found. So I had a very similar issue and everything I tried never worked until I did a complete reinstall of windows 8. For some reason upgrading from windows 7 royally screwed up my video card performance and even running a driver cleaner and re installing driver never helped any. Not sure if you upgraded from windows 7 like I did, but a complete reinstall might be your only fix unfortunately.