Raedon HD 7700 keeps crashing

ever since i bought this card there has been issues, i would play call of duty or bf3 and i can play for 30- 40 minutes but after that the game freezes and the display driver just stops working   then the game closes and the desktop says 'raedon driver stopped functioning,   and then the game is unrecoverable unlike my old nvidia i sold online, with my nvidia i could underclock it then get back into the game, now the raedon fails to work after,   i have been having this error a lot and it pisses me off, i only had one time when i could play a hour uninterrupted before being ushered to the freeze of death, i tried everything, underclocking, updating drivers, same thing every time, it is so stupid, my specs are

Amd Phenom 1045T 2.7 Ghz Cpu
600 watt Thermaltake TR2 PSU
8 Gb PNY 1333 MHZ ram DDR3
1tb HDD
gigabyte HD 7770 OC Rev 1.0

Nothing works!   Some guy told me that the card is undervolted, is this true? the voltage is 1.238 Volts
Thanks