Low frame rate and GPU usage :: American Truck Simulator General ... https://steamcommunity.com/app/270880/discussions/0/3770113546996754836/

>No matter how good your computer is there will always be framedrops on ATS/ETS2. It is on an old engine and doesn't utilize CPU very well, which it turn will hinder your GPU's ability to turn out more frames.

フレーム落ちはゲームエンジンの仕様上もうどうしょうもないっぽい？
バニラ環境で、discordをシャットダウンしてどう変わるか見てみるか