Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Status
The first post of this thread is a WikiPost and can be edited by anyone with the appropiate permissions. Your edits will be public.
Maybe you need to remove and reapply post-install root patches because the Nvidia card needed patches which cause problems for the AMD drivers now?
Good idea, but I have no keyboard or mouse access immediately after I am able to log in on the problem cMP

However!

I do have a second macPro 5,1 with the same AMD Radeon Sapphire RX580 Graphics Card, so I'll attempt to do that with the drives on the macPro 4,1-5,1, assuming the post-install root patches are applied to the SSD drive with the OS.

I'll report back soon in case this helps anyone else who ends up with a similar problem.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.