To be honest, I don't see a problem in your picture.
The temperatures are fine (graphic cards are able to get 70°C)
On the other hand, looking at the patern of the graphic your GPU tends to go immediately stop.

My guess: Putting the graphics together I think your computer stops the GPU usage as soon as the temperature gets to 60°C and starts again under the temperature of 50°C.
I thought that you could highten this temperature.
Note that this is just speculation...