Hi everyone, I am having the above issue with my Mac pro that has been flashed to 5,1, and has also received all the latest firmware patches needed to run High Sierra and Mojave. So the issue that I have been trying to work around for a while is that the RX 580 worked fine in High Sierra, but refuses to work in Mojave at any capacity. I cant get video during the USB install with Mojave, where pretty much any other version of macOS works fine from a USB installer. To get around all these problems, I simply did what a lot of guides and posts suggested. Which was the following: Upgrade the firmware with the High Sierra Installer and reboot Upgrade the firmware with the Mojave installer and reboot Make sure High Sierra is updaded to 10.13.6, and run the Mojave installer from inside High Sierra Waited for it to install, it was at this point i noticed it wasn't installing Installed my GT 120 and the installation finished, and it booted into Mojave (without the fancy Metal animations and transparencies and whatnot but it worked) Put the RX 580 back in After completing all of these steps, the system will get stuck on the progress bar (what I am seeing when both video cards are installed), somewhere between halfway and 75% depending each time. I have fully reset the SMC and PRAM and these didn't have any major impact If someone has some insight into this I would really appreciate the help.