Current specs CPU- i7 6700K Motherboard- ASRock Z170 Gaming K6 Ram-DDR4 16gb GPU- Nvidia Gtx 1070 (not overclocked) PSU- 750W SSD 250GB HD 2TB

I ran Volga no problems at all on Ultra and the only time it dipped below 60fps was during extreme rain storms. I went into Caspian Desert's level and had to drop the game from Ultra to High due to fps issues but it ran particularly fine when dropping to High which I was okay with. However, Taiga runs like absolute shit on High settings. I'm constantly dipping below 60fps and I'm experiencing a ton of stuttering too. It's odd too because the fps drop is lowest 50fps but it feels like I'm at 20fps whenver it dips there. I currently kept the settings on high and when it's not dipping I'm averaging anywhere between 90-120fps outside and well above 140fps in houses or little huts. I just want to be able to enjoy a stable enjoyable experience like I did in Volga. However, I don't understand at all how with my specs I can't even run this at Ultra at 1080p. If anyone has suggestions I'd love to hear them.