Please head over to the main thread for stuttering (the thread got buried over the past 12 hrs). There are several fixes that the community has found for this issue.
Additionally, review your main Diablo IV install folder for a file named “FenrisDebug.txt”. If you’ve got a ton of ‘[Game] RefreshAudioDevices’ entries at the same intervals as your stuttering, then you have the issue that the majority of us were experiencing.
For me personally, switching network profiles worked. Go into Network Status > Properties > Network Profile: ‘Public’ - Your PC is hidden from other devices on the network and can’t be used for printer and file sharing.
There are various theories as to why this works within that thread. Can’t guarantee that this will fix your issue, but it’s worth a shot… worked for me and several others.
Good Luck!