First thing, if you're using high speed memory, make sure you're on at least BIOS F5 which applies the SOC voltage fix for this board.
What were you seeing for your CPU temps before you set the throttle temp to 83c?
I'd check the powersave settings in the BIOS, and assuming you're using Windows all the power settings in that too (especially under advanced.) If you have a UPS connected sometimes systems will think they are laptops and adjust their power profiles accordingly.
I'm on Linux so getting it to stop going to sleep was an annoying process, but now it runs all the time forever!
Though that's only if it isn't some other issue. Is it about two hours or two hours exactly? I'd time it and if it's a solid two hours every time then it's probably a power management issue.
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