the above is because you have overclocked too much. startthe mem overclock at 100mhz run for a few days and see if this occurs and beleive me this will not happen . you need to find that one card that is moaning...
Thanks and Ive been trying to reduce it each time but not getting it right. I finally tried to limit power to 85%, core +100 and memory +650. Been running for more than 5 hours without issue so far.

for nvidia cards set power limit to 68%, gpu oc to 0 and mem to about 200 then 300 then 400 till it crashes.