CPU core temp is being reported incorrectly. 287C is way too high to be real.
Package temp and CPUTIN look like they're probably accurate...warm, but within
spec. A more stressful load would probably cause thermal throttling or temperature related instability, but I don't think that's the case in your games.
GPU temp looks normal. Most GPUs have a target temp in the 75-90C range (depending on specific part) to keep fan noise as minimal as practical, and no GPU I am aware of isn't speced for at least 85C, with most being able to go higher before there are issues. However, if the PCB/memory/VRM isn't cooled properly, that could certainly cause issues as well. When is the last time you cleaned out the video card cooler?
I'm leaning toward a GPU issue because of that problem with Windows' 3D acceleration, but you'll need to do some testing to know one way or another.
Can you run
OCCT's 3D and VRAM tests and have them check for errors?
I saw there was no rear exhaust fan in your previous image of your cooler. Are you saying there are no case fans installed at all? That could well be a problem.
Have you tried running the system with the side panel off?
Can you take some pictures of your system that show all of it's components?