do you have any monitoring software installed like msi afterburner or precision-x? use something like that and see what temps/voltages/clocks your gpu is running at in game. Also, make sure the 6 or 8pin power cable (not sure which your card uses) didnt come disconnected from the card. It may sound dumb, but even the best of us have overlooked dumb things during normal upgrades/maintainance. I once rma'd a motherboard because i forgot to plug the 6-pin power cable on the psu side of the cable (i have a modular psu) doh!