I doubt it is a heating problem. - If it were then you should be getting freezing in all games, not just Warcraft.
Could you post the make and wattage of your PSU and then,
Download Everest from here:
http://www.majorgeeks.com/download4181.html
and SensorsView from here:
http://www.stvsoft.com/SensorsViewPro21Setup.exe
Use them to check your temperatures when you first start up and then after you have played for about 30 minutes.
Also check your PSU voltages and post them here with your temperatures.
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Confront the evil river you can't control
Wicked ways and venomous eyes
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