Rise of the Tomb Raider FPS issues.

I am playing through with everything maxed testing out my new GTX 1080, v-sync on, 1080p and mostly its 60+ but a few areas in the game bring it below into the 50s and one or two mostly the geothermal valley (the bit of green after the underground ruins) gets drops into the 40s in some areas consistently while in that area. I am kind of disappointed considering the cost of the card, is this an optimisation issue with the game or is the card underperforming? I don't think it should be a card issue considering I get 19000+ in fire strike.