I have two guys in my squad that had installed Turbo Tax this year, and because of the updates still rolling in they have not uninstalled it. Turbo Tax leaves an Intuit process running that will seek updates every now and then and that will cause the game to freeze and/or minimize. This is one of the reasons Skuzzy says you do not want Intuit anything running on your system.
Not that Intuit is your problem, but it is one example of what could be the problem.
If you are using shadows, and in particular smooth shadows? It's likely a memory issue, also. 275's are sweet, but not enough to run smooth shadows of any size.
Whatever profile you are using? I would set everything to application controlled, and set everything in AH. After you get everything set as you like it and getting smooth frames, then you might turn Anisotropic up to 2x or 4x in the Nvidia AH profile. Considering your cards everything else should be done by AH. Actually, that's probably the best approach for any card, unless you just like to see how far down the rabbit hole you can go.
