|Those numbers appear to be OK. |
Graphic cards are actually like two cards in one. The first, the one you used to view PC Health, is a generic VGA display. Once the operating system starts and loads then the full featured, accelerated, version kicks in. That portion of your card is probably damaged.
You have identified the most likely cause of the damage. Overheating.
What size case do you have? mini, mid, full tower? Does you case have a rear case fan?
Do you keep your computer case in a computer desk, or any type of confined area?