I have also noticed my framerate dropping from 60 to 45 ish in completely random spots without much going on. I hope it's not my computer cause that would make me sad. Like even the inn in the Gilded Vale made my fps drop sometimes, but other times it would be a solid 60!
Sapphire R9 270X 2GB "Toxic" Edition (not sure if that's relevant)
Amd A8-6600K 3.9 Ghz
12GB Ddr3 Ram