I picked up a Mac Pro 2012 with a fresh High Sierra install. It has a flashed Radeon R9 280X 3gb (2x Mini DP, HDMI, DVI) video card installed. I'm hoping to have 2 displays attached (neither scaled or using adaptors). First is a Dell 1920x1080 (rotated 270 degrees) and it works fine with a Mini DP/DP cable, though the screen does not rotate until after log-in and I can live with that. The other display is a LG 2560x1080 ultrawide display and only produces a black screen with a Mini DP/DP cable. It seems to be recognized but nothing is displayed. I get some scaled resolutions through DVI, but not the native 2560x1080. I do get 2560x1080 with a HDMI cable but I'm hoping to use displayport. Any ideas? I've read issues with Sierra/High Sierra and scaled resolutions, but I'm avoiding them. Thanks!