So currently in Windows 10, running Action! 1.31.3.0; you're unable to record at 120fps with a 1920x1080 screen resolution. I've tested and it works completely fine with 1280x720 etc.
On Windows 7 I used to run Action! 1.22.1 and I could record 120fps 1920x1080 completely fine and all audio and video would match up.
Here's what an average clip looks like when dragged into Sony Vegas 13: http://prntscr.com/bng0ow
On Windows 10 you're unable to run 1.22.1 and forced to run the latest version with bugs such as this. Hopefully in the next version release, this problem is fixed and I will be able to run 120fps on 1920x1080 again, because playing a 1280x720 screen resolution isn't the best.