Well taking out one stick is free, and you can probably borrow a kit from a friend or friendly nearby Carbie.Not yet. That's an expensive thing to test without being sure what the cause was.😅
Would be weird though, what made you think of ram?
The fact that your issues persist despite the new GPU means that it's not your GPU. Out of mobo, CPU, boot drive, PSU, and RAM, RAM is the easiest to test and rule out. If that doesn't work you'll have to test the other components one by one to see if it fixes the issue.