I had a similar problem when I went from 3gb to 8gb yesterday. I didn't see the dark textures but every time I would look at a tree, for example, I would see a very low rez version of the tree which would then shift to mid-rez and then high-rez. Nearly everything was doing this and would continue to do so when I turned around.
Reverting my GTX275 to the 182.x drivers fixed it.