The WHEA errors related to the hardware. And either the MB or PSU may cause the problem.
1) The MB ( GA-78LMT-USB3 Rev 6.0 ) does support the fx8370 in theory, keep in mind it has only 4+1 phase power, so it will not support the fx cpu 8 series properly. You can find the similar problems online. I don't know what other cpu you had, because you said you test with other cpu too. If you had the fx 6xxx, then use it.
You can test them like this: boot into the BIOS, disable few cores, also remove the rx 580, use onboard ATI Radeon HD 3000 graphics. If the PC does not crash, then try to enable the cores to see what happens.
2)
This only started happening after installing new GPU, the RX 580 but i tested on another PC and no crash.
Did you use the same PSU with the rx580 in that PC?
For the PSU, test like this: if the PC runs fine with few cores disable with onboard AMD iGPU, then add the rx580 to run the PC again.
Also may boot into the BIOS, in hardware monitor section ( or in PC health monitor section), check the +3.3V, +5V, and +12V, you want to see those voltages are within +/- 5%. Like +3.3V, it should be within +3.1V to +3.4V. Otherwise the PSU is not good.
3) You may update the AMD chipset driver
https://www.amd.com/en/support
4) Also use DDU to uninstall the GPU driver in safe mode, then reinstall the GPU, but you already reinstall the win10, so the GPU driver may not have problem.
DDU https://www.guru3d.com/files_details/display_driver_uninstaller_download.html