Disable core unlocking in your motherboard BIOS, that can interfere with temperature readings (and shouldn't affect any overclocking). Are you doing ANY overclocking at all though? You said overclocked to 3.8Ghz... Here's what I recommend you do.
Reset your motherboard BIOS via the jumpers to completely clear settings/any errors it may getting. I mean it, jumpers only, don't do it via the BIOS screen, the jumpers will always wipe it clean. Boot into Windows with your default settings and see whats going on (do not interfere/change any settings in the BIOS yet). You need to diagnose this problem without any overclock/BIOS changes to see if this is something serious first. If everything seems OK, then this sounds like an overclocking/stability issue.
If that's the case, start from square one and redo your overclocking. You said your core multiplier is throttling, do you have it set to AUTO? If you do, you need to set this to the highest value possible (should be 13.5 or so for a locked AMD multiplier). If you leave this to auto, your PC will not keep it at the highest setting. Motherboards/Hardware/Windows and a combination of all three dislike overlcocking... even if they are built for it, they will resort to lower numbers whenever they can,. You need to set that number to manual.
Get things going back to your 3.8Ghz and then Prime 95 test for several hours. Honestly I don't think updating/reverting your BIOS to newer/older versions will work. Your rig probably wouldn't even run if there was a compatibility issue there. Try what I recommended and see if it works.