I don't even know what VRM is. That's probably a bad thing. I saw that number and was concerned as well...it didn't budge the entire time I had GPU-Z open, so I'm not sure what to think of it.
If anything was 255c in there I'd be able to physically feel it when I put my hand on the card, wouldn't I?
Oh, I almost forgot. I tried to turn down the voltage in MSI Afterburner, but every time I touched it, it crashed.
Being that the VRM is up at 255 I would say your having some sensors issues. That's pegged showing that a sensor is misreading. If you were really at 255 there would be smoke coming out of your computer. Lol. That's like 500 degrees F.
I run a 7950 at 1100 MHZ and 1.31v and my temp's dont get over 56c under gaming load, for a reference.