I just updated GPU-Z to 8.0 and found something very interesting on the history:
http://www.techpowerup.com/downloads/2418/techpowerup-gpu-z-v0-8-0/
Any of you having troubles were running an older version of GPU-Z?
My 290 vapor-x wasn't affected by this, but maybe it's the combination with...
Temps are ok?
Maybe a bad contact? Try unplugging it completely (power cables and all) and reconnect.
Otherwise, try uninstalling the drivers with DDU.
Download and read instructions here:
http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
And then install the latest...