I'm probably doing this wrong. I swapped the stock ATI Radeon HD 5770 GPU for a RX 460. After several reboots, I put the stock GPU into slot 1, and added the RX 460 to another slot, to check for errors. At boot, the system was displaying a kernel panic message, then restarting. I'm aware that this card won't show the boot screens, but I'd thought this GPU was supported with 10.13.4. What's the next step for this?