If you have the proper driver installed for AMD, and you are running the proper kernel version for support of your hardware that doesn't have the regressions that Aravisian speaks about.
Michel mentions if you have power saving enabled on the AMD card. You can install the extension bellow to allow you to change the power performance levels of your AMD GPU.
https://extensions.gnome.org/extension/1079/radeon-dpm-control/
For general disabling of power management, you can do so by entering the following commands.
CTRL ALT T to enter terminal.
xset -dpms





