My GPU reaches 90C under load. Is that too hot?
Yes, and while the GPU can take that temperature, it isn't good to run your GPU at that temperature. You probably have dust clogged in the heatsink fins of the GPU & CPU and also the front intake and back exhaust ports. I suggest a can of duster that is approved for use on electronic equipment. Pay attention to those heatsink fins.
Of course there is no guarantee that will fix your problem, but your GPU will love you for it.