Try I/O of 3.4. It might be my PS, but at 3.3 it doesn't seem to run very stable (I AM OC'd from 700 to 981, but I seem to remember having to set that to run stable at 700). Sorry I forgot to mention earlier. Who knows if it will work, but it's worth a try, and I have heard of people running as high as 3.6, but I don't recommend that (Mostly just because I haven't tried it myself).
Maybe the mem is getting too warm (Rare, but pos.), and needs a little more V to cut down on E-migration. This will also help the vid card and sound card I think. I think they use the 3.3V and the 5V curcuit. I have heard of some TNT2U's needing plenty of power. This was a problem when the SS7 platform was maturing if I remember correctly. Of course, I could be WAY off base too
PS - My PS is an Antec 300.