You said about tried graphics card drivers so I assume you mean updated, but had you recently updated them before this started? If so perhaps try going back to an older version. When it comes to graphics card drivers newer isn't necessarily better as they can introduce new problems and in most cases unless a specific problem/bug is mentioned in the driver notes, there isn't really going to be any performance increases after the card is about 6 months old, it'll be about as optimised as it's likely to ever be.

Also is your graphics card one that is pre-overclocked? As in it came already overclocked by the manufacturer. I only mention this because I've seen posts pop on up on this forum before where people with pre-overclocked cards had issues and had to essentially underclock them to make the game stable. I don't know if this is your problem or not, seems strange if it only just started happening, but trying to give some more options.