According to the latest release from the FCC, Cox's typical levels of packet loss are ~0.1%. This is a typical amount of packet loss for a cable provider:
However, they seem to have either serious hardware or software issues with their infrastructure. In my area of Phoenix, during peak times I'm seeing anywhere from 8-30% packet loss - which renders my internet unusable. This has been occurring for over six months and still continues. I'm seeing the exact same issues as you.
I also have the exact same modem, and I've cycled through three different new models to rule out issues with my hardware. Went through four routers as well, all brand new - same symptoms persisted through all hardware replacement. Cox replaced my entire RG6 line from my modem to the nearest neighborhood node. They refuse to do anything else and say that my experiencing 8-30% packet loss during peak times of utilization is what qualifies as "best effort service" to a residential account. This is all while hard wired.
I would advise contacting the FCC and filing a complaint if this issue persists.
