Ok so I ran GPU-Z and during the game it stayed at 0.9V most of the time sometimes jumping to 1.05V, the HIGHEST it got during the game.
May be overclocking did something to it. There may be two reasons, either bad power supply or it overclocks itself during gaming, note its core clock and memory clock usages in GPU-Z while you were playing game,were they overclocked during game? Try to run it in other PC. Or if you can increase voltage try to do that also.