Did you try xf86-video-ati?
You could also try without xf86-video-anything to see if the built-in modesetting driver gives you the resolution you need.
If you take a look at /var/log/Xorg.0.log you should be able to see which drivers Xorg tries to use ...
You could also try without xf86-video-anything to see if the built-in modesetting driver gives you the resolution you need.
If you take a look at /var/log/Xorg.0.log you should be able to see which drivers Xorg tries to use ...