Question Low fps after GPU upgrade

Mar 21, 2020
My set up:
CPU - FX 8370e
GPU - RX 580 (upgraded from gtx 950)
RAM - 16GB
PSU - 550W
So my issue:
With my gtx 950 i had like consistent 100 fps in league of legends, 80+ in CS:GO and etc.
I upgraded to an RX 580 for the quarantine and suddenly my fps in CS:GO changes rapidly between 60 and 120, League fps is 120 at most and drops to 40 in fights with a lot of action. Lowering the graphics makes no difference, so i do not think this is a CPU bottleneck issue, with everything on very low in league with the 950 i was getting 144+ fps. Some other games however run fine, like APEX legends where i get 120 fps consistently.
What i tried so far:
  1. Updating the BIOS
  2. DDU and reinstalling the drivers again
If you have any ideas about what the issue might be I'd be happy to try them out, it's really frustrating to stay home 24/7 and not be able to play anything.
Thanks in advance.