Framerate Problems

When I open DST, my computer switches to 60 Hz (down from 165 Hz). It won't permanently let me change it in game settings even though the option is there. It just automatically switches back to 60 after I set it to 165. After I close the game, my computer automatically switches back to 165. Regular Don't Starve doesn't have this problem. Monitor is Dell S3220DGF. Relolution is 1440p if that is relevent. GPU is nvidia gtx 1660.