Am having lots of trouble since 3.1 too.

Am using a GTX 260 and been running 4 clients without any problems pre-patch (one 1024x768 @ high settings and three 800x600 @ low settings). Well, now am getting lockups while doing the argent tournament dailies. At first its a few seconds freeze on all clients. Those freezes get more frequently over time and finally lead to texture clipping issues. After a while one or more clients will perma-freeze or crash.
My graphics card isn't overheating, it's running @ 60°C. I didn't change anything except of applying that crappy 3.1 patch...