100c your on the verge of killing the card due to heat.
Your going to have to strip the cooler off my friend and clean all of the thermal paste off the Gpu die, re apply some good quality thermal paste spreading it in a thin layer across the Gpu die and any other Dies that contact with the cooling plate. clamp it all back together so it tight.
Make sure the fan is spinning on the card also. And give it a good dusting