4del

I can't tell where the sudden shift in temperature came from but first make sure that the airflow in your case is good, it could be getting heated up because the fans aren't working and it's just recycling hot air.
If this doesn't work, I recommend taking the GPU apart and reapplying new thermal paste as this actually does increase your performance by alot, but keep in mind that it is voiding your warranty.

Thanks a lot mate.