Stuttering when using Fullscreen, but not when using Windowed Fullscreen

So, I decided to get back to playing D3. I have MSI Gaming laptop MSI GT75VR7RE GTX 1070m/17-7700HQ, 16GB, 120HZ. Right now it’s hooked up to an external 4K TV 120HZ…Tried using just the laptop, that makes no difference. I’m noticing that as if I play the game in fullscreen mode, the game stutters every 30 seconds or so, but if I switch to Windowed (Fullscreen) the stutter goes away. Can anyone tell me what’s going on here? I’ve tried starting the game in 32 bit mode, disabling full screen optimization, disabling/enabling VSYNC.

Thanks,
Mike