Hey man, I had the same problem yesterday with my XFX 5770 and when I played a game it kept crashing. Looked in ccc and my temp was 100 degrees, idle was a 60. I found the problem and just done a google search to help other people, so I found you now Here's the fix:
Open the graphics card up and remove the heat sink that sits on top of the gpu, the part of the heat sink that is facing the fan builds up a lot of dust, so much so that it blocked almost all the air that the fan is trying to push out. At first when I open the card I thought there wasn't a problem because you couldn't actually see the fins on the heat sink that is facing the fan. I guess you could call this a bad design of the graphics card. Just remove the dust particles. There'll be thermal paste on the gpu and the heat sink, I didn't reapply new paste because I don't have any but it still worked like a charm when I put it all together. Happy New Year!