Hi man,
I was looking around to see is BIOS 13 support G2 stepping Atlhon X2 CPU´s. Look ok to me but there is a small thing that could be your problem.
In the CPUz the Stepping of your CPU is BH-G2, and in this link the supported stepping CPU´s are G1 and G2, there´s no BH- before each one
http://www.abit.com.tw/cpu-support-l...thlonX2d-b.htm
Could be a Stepping issue that you are facing right now, Intel and AMD are always doing small changes to the cpu´s so this 'little' temperature glich could be a BIOS issue with your current CPU. If BIOS 13 support your current stepping, you can fix the problem.
Did you try other CPU? An older one, sry if i was rude before.
Good Luck !