My PC is 1440p, GTA V is 1440p and when the game is in Fullscreen it stutters like crazy, when I'm moving in-game. If I stand still, it's pretty alright.
If I change GTA Vs resolution to 720p (still in Fullscreen) it stutters still like crazy, but if I have GTA V in a Window (with my desktop in the background), it runs fine. But is to small of course.
Moonlight Settings are 720p60
Moonlight on the phone and tablet don't have these problems.
PC is connected via LAN. And all my devices use 5Ghz Wifi.