reply to volgon4
I went into the attic to look at the wiring, I thought maybe we had some old wires that could be causing the packet loss. It looked like all of the cables were either RG6s or RG59s. The coax cables feeding into the attic (the point of entry cable I guess you could say) from the outside and the one down the wall into the room with the modem were both RG6s so I think I'm okay there.
The tech that came out last Friday also put a filter in the attic to prevent the modem from pushing noise into the line. What cable is the filter supposed to be on, the cable that leads to my room (which contains the modem) or the cable leading to all the other rooms (which only have TV)?
An update: I provisioned the 5120 again so I could do some ping tests with it. I've had good results: 0-1% packet loss (the 1% is fairly uncommon and to be expected from time to time), normal ping and low jitter (most of the time). Before the switch my 6120 was getting anywhere from 2-8% packet loss, normal ping and high jitter (20-40ms). This seems to point to my issues being related to the modem. I'm going to keep the 5120 running for a while; I had separate issues with that modem (it rebooted randomly) so I'll keep an eye on the modem logs.