It could easily be a software issue. I notice that your clock speeds in GPUz are dfferent from each other, that is a little strange. I would completely uninstall all graphics drivers, reboot and freshly install the new ones. There could be some old .dlls and bad leftover configurations from your old card.
Once you do that, make sure you go into the CCC and move the powertune slider all the way to the right. Try both of those things and see what happens.
Let me know if that works