So I currently have a late 2009 Mac Pro that I upgraded to a MacPro5,1 w/2x 3.33Ghz procs. I've been using a Radeon HD 7950 for awhile now and have already updated to Mojave 10.14.1. But I just recently picked up a "Sapphire Pulse Radeon RX 580 8G GDDR5" on eBay and have been trying to get it to work in place of the 7950 to no avail. I thought this particular card was one of the ones supported by Apple, correct? But when I install it, computer boots up fine, I see the fans on the RX580 kick in, but then like 20 seconds later they stop, and that's it. I'm feeding the card the extra power it needs with a 2x Mini-6 pin to 8-pin cable. I normally have 3 displays connected but I'm just trying to start with one right now. I tried each of the 2 DisplayPorts as well as the DVI and nothing has helped. Anyone have any idea what else I can try to get this working? Or is a problem with the vid card itself? On a side note, I noticed that even though I'm running 10.14.1, my Boot ROM version is still 138 instead of 140. And I can't update it to 140 because of the Metal detection bug whenever I try to run the full Mojave installer. Am I missing out on anything by not having 140? And if so, is there any way I can get it to install w/out somehow going back to High Sierra?