GPU only works in x4 slot on HP ED 800 G3 SFF

EDIT: After days of fiddling, I made this post and went back to troubleshooting. It just booted with no problems. Scratching my head, but something I did in passing was the trick. Now to make sure I save these exact settings!

EDIT2: It turns out it was always working, and it is just BIOS/UEFI screens that will not display. This kept me from installing my base OS at all until I moved the GPU to the x4 slot. Since I installed the OS with the GPU in the x4 slot, now it boots to the point where I enter my luks encryption key and I'm good, but it still won't show the BIOS screens. Perhaps I need to enable the legacy Option ROM for video?