After doing the above update to my machine the display looked fine but movies would not play very well. So after numerous re-installs of Ubuntu 15.04 I followed the install instructions on the amd site. Note this is for my AMD radeon R9 380 gpu. Please scan through the install instructions that you might find on the site below. It should be as I have it here.
http://support.amd.com/en-us/download
Note that there isn't just 1 file to download. You need to download 4 files, in my case yesterday they're as follows:
fglrx-core_15.201-0ubuntu1_amd64_UB_14.01.deb,
fglrx_15.201-0ubuntu1_amd64_UB_14.01.deb,
fglrx-dev_15.201-0ubuntu1_amd64_UB_14.01.deb,
fglrx-amdcccle_15.201-0ubuntu1_amd64_UB_14.01.deb.
Then check that there are no legacy drivers on your system with the follwing cmd
sudo dpkg -l fglrx fglrx-core fglrx-amdcccle fglrx-dev
You can use the following to remove them. Note after the below cmd might not be a good time to reboot your machine ;)
sudo dpkg -r fglrx fglrx-core fglrx-amdcccle fglrx-dev
My terminal session gave an error message that fglrx-dev was unknown to my system, so I removed that from the above command
I placed all the files into a single folder, in terminal I navigated to that folder and once in that folder I ran the following
sudo dpkg -i fglrx-core_15.201-0ubuntu1_amd64_UB_14.01.deb fglrx_15.201-0ubuntu1_amd64_UB_14.01.deb fglrx-dev_15.201-0ubuntu1_amd64_UB_14.01.deb fglrx-amdcccle_15.201-0ubuntu1_amd64_UB_14.01.deb
There were no errors reported in ubuntu 15.04, which was a newly installed build.
I can now watch movies in VLC, which for some reason now plays better than xbmc and kodi. Strange as my old underspecced dual core machine was the other way around. After installing steam we played 2 games, not very gpu intensive, i.e. Dota and TerraTech. I can see that Ubuntu is not getting the most from the gpu. Will still be trying out other games, but good luck
sudo apt-get install fglrx-updates
and reboot.