Sounds like the same problem I had when I upgraded to a 3080 last year. I had to upgrade to a much bigger case with better air flow. The other issue that causes this problem GPU sag. That is the the 3080 and 3090 are so big that they actually put too much weight on the motherboard and don’t sit properly. I had to buy a GPU brace to support my big 3080.
After I did all that I didn’t have any further issues.
This is the brace I got. Doesn’t cost much https://www.cclonline.com/gh-01-a-rgb-deepcool-gh-01-a-rgb-gpu-stand-bracket/?gclid=Cj0KCQjwm6KUBhC3ARIsACIwxBhqOOxllAiFD1Oznbv5Qwj_t40vgPH_RMmZ5rD5XLeo2BklTJDZdBUaAvYaEALw_wcB