Just this minute found out what really has been causing my stutters. Ive been blaming my router, so I switched to my old Apple Airport Extreme and haven’t been having any problems until today, when I re-connected my printer to my router via WiFi. As soon as I did that, same stutters every 72 seconds. Switched my printer off, stutters gone. So it’s a communication issue between my printer and my router which is causing interferance.