This update seems to have significantly improved my recordings. The desync is practically gone, though I've noticed a steady desync once I get up to 30 minute + recordings. However, I haven't tried any recordings longer than that, and the desync is down to less than half a second as opposed to 30 seconds or more.
However, I am getting a weird issue when exporting. Despite having both the game audio and commentary audio in the Action player (I can cycle between them with the A key), when I export the video and run it in another player like Windows Media Player, the game audio is silent and only the commentary audio plays over the video. When I import the exported video to Sony Vegas for editing, there's no video at all. Just the game and commentary audio.
I've been able to convert the file to different formats, giving me the entire video and the two audio files I need, so there is a workaround for me, but I'm just wondering what could be causing this.