I’ve noticed that certain areas of the game (specific areas of junktown for example) will cause a major drop in fps, but a simple alt+tab will resolve the issue.
I have a gtx 1080 with an i5 6600k, 144hz monitor and I run msi afterburner / rivatuner. I am also running the GOG version if that matters.
let me know if there is anything else I can report that would be of use.
Cheers!