that can be virtually anything. from broken GPU[from failing fan to broken GPU itself] to overrated PSU[which is more frequent].
diagnose further w/o more input is like cure via phone attempts.
can you post screenshot at least ?
and/or did you tried monitor voltage ? preferably not only by software, but hardware[ie using "multimeter']
Well. I think I figured out the problem. My 6950 profile saved the memory speed to catalyst control center. So all 3 had OC'ed memory. I didn't notice because frankly I don't know the stock memory rate on the 6870.
After I tuned the memory back down (I noticed after doing some trouble shooting), everything seems to be working fine.
I'm getting about 275 mh/s per card at 940.