usually i use 120 fps i just tried at 60fps and still froze. i started speedran to check the tempatures and after about 2-3 minutes ingame the core temp goes above 45C and has a red arrow next to it so it definitly sounds like an overheating issue.
Tbh it doesn't sound overheating at all. The current generation and last generation gfxcards are fine with up to 95-105C temps, at only these temperatures will they start throttling speed. If you check any gfxcard reviews, you will notice this by yourself as most reference design gfxcards heat up at 80C or more these days, it's only those gfxcards with custom cooling that are cooler.
Since you have an AMD card and you say your other games work fine, I suspect AMD's opengl icd is a piece of shit and fails for whatever reason. Or maybe your system is otherwise unstable? Or perhaps the card is broken?
You can easily test your computer's stability by few programs:
1) Use prime95
with torture test
-> small fft
test to test your CPU (45-60min of torture should be ok). Just remember to enable error checking in the menus. You will get an error if something goes wrong, this usually doesn't crash your computer.
2) Intel Burn Test
with the highest setting (uses all your ram) is a good indicator for memory/cpu/system stability, just run something like 10-20 iterations (this should last for an hour or so). Again, you will get an error if something goes wrong, this usually doesn't crash your computer.
3) If you get an error with either of the prime95 or IBT, you probably want to check your memory by using Memtest86+
, just burn it on some RW disc and reboot from it. Few passes would be ok in this case, you will be shown errors if there are any.
4) Finally, you can leave Unigine Heaven
to run for an hour or so to test your graphics card, just remember to maximize the settings (well you can use the second highest tesselation setting) so that it will heat up your gfxcard enough.
Just a note: when running prime95, you can use your computer to do other stuff, prime95 is fine in the background. IBT on the other hand is not such program, as it will use all available ram under the highest setting and makes your computer slow as hell, so you will be better off to leave it running on it's own. Obviously Unigine Heaven should be run on fullscreen, so unless you like to watch it, you should figure out something else to do in the mean while.
If none of these programs give you an error or crash, your hw is probably somewhat stable, but the problem would be in AMD's drivers.