It seems there are some configuration problems with the NVidia drivers and GTA V. I was reading around and found that if you change your "Power management mode" setting in the NVidia Control Panel, from "Adaptive" to "Prefer maximum performance," that my problem went away (at least for my last play session.) http://nvidia.custhelp.com/app/answ...ent-mode-from-adaptive-to-maximum-performance
As a general rule, you always want to set this to prefer maximum performance otherwise your GPU is not running at it's full potential.