Help diagnosing internet problems

I am experiencing intermittent slow speed problems (video buffering, slow downloads, etc.). I have the preferred internet service. I would like to make sure I don't have any issues I can fix myself prior to the service technician visit I scheduled for Friday. First, installation was 1 month ago. The service techs warned me that the cables inside and outside the house all looked old and might need to be replaced. During the visit they only changed the ends of all the connectors, removed splitters, and added attenuation. They also removed a section of cable that was chewed on by something. I have a new SB6141 cable modem. I'm not sure if it has the latest software. I logged onto 192.168.100.1 but I don't see where it lists software versions. I have removed my router from the mix as well but not much difference. Primarily I am downloading video lectures for a class I am taking. Downloading the same video with my laptop at a relative's house (5 miles away and he has the same internet service and modem) the download is lightning fast compared to at my house. The Cox speed test is all over the place day to day. Sometimes as good as 20 Mbps and sometimes as low as 4 Mbps.