Thanks all. Pretty sure the card wound up being a dud.
At first I just did the card swap. It recognized the new card without a hitch and all seemed well with the world. Well, five minutes into trying it out with Civ 5 it crashes. Then I tried Fallout 3, which froze up a couple times. Afterward, even just on the desktop, the driver kept crashing and recovering over and over again.
I uninstalled the drivers, ran driver sweep in safe mode, and reinstalled them... no luck, same problems. Did the same routine with the latest beta drivers... no dice.
I uninstalled all the drivers, put the old GTX 275 in, reinstalled the drivers, and everything was fine again.
I suppose the card was bad. I'm using an Antec Truepower New 750W power supply so it was definitely getting enough juice. Can't think of anything else it could've been. The computer has been solid stable otherwise lately.
Oh well, the shop refunded it without a fuss. It was an MSI card. I'll think about getting an EVGA card or just waiting to see what AMD's lineup looks like later this fall.