what drivers are you running?
I don't have the card, but when I was testing it was 306.23 I think. Not to reiterate the whole story here, but I used exactly the same drivers and system with my evga ftw 670 which has no issues. The gigabyte card is faulty, was found faulty by gigabyte who replaced a chip (described above), but the card still has all the same symptoms and is not fixed.
I need to know where I legally stand here. The vendor (not ocuk) has shipped the card back (!) (just got parcel force email). Help!