My game starts smooth but degrades over time.... I noticed the gpu downclocks from 1950 mhz to 1500s in certain places(cities) while gpu usage stays around 30-60%.It's not a temps problem either,the card isn't breaking 65C.I think there is something wrong with the engine or the game. Playing in fullscreen/max performance doesn't help either.The game always end up starting smooth then degrades into a choppy mess.
I play with a gtx 1080ti strix/i7 4790k on 1080p
*Update" restarted the game and did a good 1-2 hours of smooth playtime but at one point the game downclocked to 1569mhz from 1947mhz with around 60-70% gpu usage and for some reason it stayed downclocked to that number til I restarted.(it doesn't adjust the clock back up for some reason) the game was having long freezes on looting at this point.