Hello,
Here is my story, maybe the information helps for someone...
A few months ago I experienced the 'GPU driver appears to be hung' problem almost every day. So, I brought it back to the store. Two weeks later I went back to pick the mac up, they said the D300 GPUs were replaced. That evening, I think it took about 5 minutes until the spinning beachball was there again. So I brought the mac again to the store and said that the issue was still there. Three weeks later (I think June 25), I received the mac again but this time the employee said he didn't receive information about what the repair center had done :/ Back at home I had to configure OS X again so I assume they just reinstalled OS X this time. Surprisingly, the issue didn't came back until yesterday. And it could be coincidence, but yesterday I installed El Capitan 10.11.6.
At this moment I think that the graphic issues are related to the OS version (in my case 10.11.5 was a good one then). Any thoughts on this?
I recently bought a Mac Pro 2013 and sent the first one back. I purchased refurbish to save on costs. The second one seemed to work better, but noticed a few graphic issues when using FCPX. Called tech support and they said they would call me back...never did. But while I was waiting 10.11.6 came out and to my surprise it fixed my graphics issues.
Here are some suggestions:
1. Find out the date of when your system was assembled (mine fortunately was April 2016-or at least repaired). Look on Internet for small program to collect info on your system.
2.make a USB OS X 10.11.6 install drive to use to install. Download the latest version from App Store.
3. Reinstall OS X 10.11.6 from scratch, boot into repair mode before, wipe disk clean first.
4. Install OS X from USB
If problem still exists, then download the 10.11.6 combo update and apply. Don't use the auto App Store update.
5. If problem continues, apply the combo update again (sounds funny, but try).
This fixed my issues and my Mac Pro is happy. But runs hot (expected and is normal unfortunately)
If your Mac Pro was assembled in early 2015, then get the graphics card replaced. Look up the recall on the Mac Pro 2013 for more info.
I think the apple tech did not call me back because he knew that the update would fix my issues that was coming out in a few days. He said that he would do some research on the issues I told and call back. Of course he could not tell me that the update was coming in two days and probably waited for me to call back if issues after apply update continued.
These steps helped my issues and hope it helps.