Could be many things. I did note that you mentioned that your modem is two years old. Sometimes ISPs have changes or "enhancements" in their services which require updates to a modem. In my case, my provider upgraded our service to a deal where the 1st 50MB of data downloaded at a very high "turbo" rate and then throttled down to a lower (but still relatively quick) rate. Long story short, my issue wasn't with the change in speed per se, but in the new protocol/language/packaging/presentation of their data. The cable modem that came free with my service a few years ago was not able to be upgraded from the old DOCSIS 2.0 standard, to the newer DOCSIS 3.0 standard they were now using. It only caused issues with some things like large downloads or streaming full length videos stalling, stopping of getting interrupted. Apparently my ISP can push updates to client modems, but mine was too old to accept the new code. They didn't contact me about this, and I spent several weels messing with DNS server settings and a variety of other possible fixes. Finally I ruled out everything on my end, called them. The first thing they asked was what modem I was using and immediately told me it was known to have "occasional reliability issues in some cases" with their signal. Anyhow, I bought a new modem at Best Buy (the ISP offered to rent or sell me a new one, but at a high price). I plugged it in, called the ISP again, told them my modem make/model and they pushed through their update - no more issues.
This may not be the issue you have, but you can probably call your ISP and give them your modem information. That would at least let you know if your hardware was part of the issue. It might save you some time even if it isn't the root cause of your issues.
Good luck, and welcome to Mac-Forums!
