You might as well set your MTA settings and CIT settings to low as GTA sa can't really handle 144 fps. So, you must try to set everything to low to avoid these problems.Head to /settings (in-game) then scroll down till you see "Shader Graphics" set Good textures, Car reflection shader, and detail shader to 145. Press F8 > type fps_limit=0.About your ping, you may head to this board: https://cit.gg/index.php?topic=158399.msg4535669#msg4535669 There are also FPS solutions there so if you want to really fix these problems you may try every solution there is from there. Goodluck!
When in game, open your /shownetstat and check if you have any packet loss. Sometimes your ping can fluctuate or rise if you have that.
Okay so the problem might be "routing". It is a path your data bytes take in a network to reach the server. Your ISP's routing has issues which causes high ping to different servers based on their routing paths.Nothing you can do except trying to restart router to reset the routing tables. (Very rare chance to work)
Yeah its a VPN, it just changes your ping server to that particular location before pinging CIT server. The routing changes in that process. Good to know it helps!Lemme know if you need any help or will lock this, good day.