So based on your description of the /netgraph results it seems you are experiencing periodic loss of bandwidth. It isn't dropped packets, or a loss of connection. If you are on WiFi, I would try switching to a wired connection and see if that helps. Check and make sure that any wired connections are in good condition and securely connected. If you have your own Router, you could temporarily bypass it and plug directly into the ISPs modem/router. If none of these seem to help, I would request, especially if it is not fairly new, a replacement modem from your Provider, most providers will not charge anything for this, and many times an older modem may have issues interacting with newer equipment on their network.