A second idea if you cannot source another gpu; Change PCIe slots. While I believe your video card is going bad or at a minimum: overheating: consider moving it to the other x16 slot on your mobo as it IS technically possible the slot is having issues. It also doesn’t hurt to spray your case out with canned air to get the heat capturing dust out.
Definitely have to do it one by one. Process of elimination!
I’ve had times where I’ve pulled the motherboard from the case, laid it on a rubber cloth and hooked everything up one at a time to find the issue. Even had one time where the mobo was shorting out on a case itself. So yeah, it doesn’t hurt to do that. Good luck!