X58A-UD3R reboots automatically once and then fine for rest of day

[newkton1]

I have an X58A-UD3R that has been running Snow Leopard, Lion and now Mountain Lion fine for years but ever since Lion was installed, it has developed a weird habit of rebooting once automatically about 20 minutes after the first power-on of the morning. After that, it runs fine all day until the evening power-down.
This is not a KP and there is nothing showing in the console logs. The BIOS reboot on CPU/Fan problems is switched off and we have checked the PSU, memory, etc., and I cannot find anything wrong with the hardware. It does the same thing whether booted from a Chameleon or Clover USB stick. The GPU has been changed from a 4870 to a 6870 and back and same problem.
Any idea what else we might look at?

 

[Hackintoshron]

Mine never did that unless I had Turbo feature on in the BIOS. Try disabling it, and see if it still does it.