Weird GPU issues on some X58 mobos with RX 7900XT and RTX 5090 (RTX 2080/2080Ti/3080/3080Ti/4080 Super all work fine)

[loki1944]

So I'm kinda frustrated with some weird issues on both the XFX RX 7900XT and the Gigabyte RTX 5090 OC not working in some X58 mobos; RX 7900XT refused to post (black screen) on i7 980X/ Asus Rampage III Formula motherboard /24GB RAM; however this card WILL post on my i7 920/EVGA X58 SLI /12GB RAM system. Now I'm running into the issue where my RTX 5090 will not post (just cycles the same two bios numbers instead of progressing) on the i7 920 sytstem; any ideas why this stuff is happening? Setting bios to default also did not resolve the issues.