Asus Ultrabook, good performance one day, bad performance the next

Hello Guys

I have an ultra book s550cb-dsex w8 ultrabook. I have Skyrim on it, a game that runs perfectly on a desktop with half this laptops specs. My problem is that some days when I play it the game runs with terrible frame rate and some others the game runs perfectly. I make no changes to my laptop between those times, I simply boot the laptop load the game and If I can play it that day I play it until I stop or If I can't due to FPS I turn the laptop off and try again another day,

It's not just Skyrim, it does this on the EIMS 3, far cry 3, tomb raider,x-com and every other game requiring somewhat decent graphics. Do you guys have any suggestions? I am not a laptop person. My last laptop was a windows 7 toshiba which ran perfectly for years until the battery went bad, this windows 8 toshiba has given me nothing but puzzles ever since I got it.

 

Also drivers up to date.

 

There are a few possibilities it could be: overheating (resulting in throttling), the AC adapter cutting out, resulting in the system running off the battery, or the drivers. Have you removed the existing drivers for the NVidia chip and Intel graphics before installing the most current?