Quick question, what does GPUZ show in terms of core and men? As well, is PCIe 3.0 @ 16x also show up? Recently I had a 570 4gb come to me with poor performance and after playing around with it (doing same as suggestions) I decided to look at its core and clock settings. Found out that it was seriously off from the standard of the Aurous series of the same card. So I obtained the ATI flash and the bios from here, flashed it, and now it is working as intended for my customer.
Can you post the GPUZ screen here please?
Also, can you list all your parts for your PC as well?
As well, when removing drivers, do it in safe mode. Run DDU (display driver uninstaller). Then reboot back into main desktop and install latest drivers. I know you said you uninstalled drivers, but I don't believe you mentioned how you did. And same DDU method should be done for both AMD and NVIDIA drivers