NVIDIA GPUs are rated FAR higher than 80°C. You have to get over 120°C to start making a good chip fail. If you're having problems at 80°C, you need to consider bad video RAMs, inadequate thermal system, or even a nonThermally-failed GPU (for example drivers as you guess).
In what manner does your video fail? Describe the artifacts or post a screen dump. I should be able to distinguish between bad GPU and bad video RAM for you, if those are your failure points.
bad pixels (shimmering, wrong color, wrong texture) on rendered objects = bad GPU.
bad pixels forming relative to your display positioning = bad RAMs.