Alright, it's gotta just be that I'm getting bogus results from pingtest.net. I ran the test you linked to above twice and got 0% packet loss and an average of around 60-70ms latency. I also manually ran some continuous pings to google.com and yahoo.com for a couple of minutes each and didn't see a single dropped packet.
It has to be something weird between the modem and pingtest.net. I had another Ubee DOCSIS 2 modem (the U10C018) prior to this one and pingtest.net never showed any dropped packets, yet for some reason this one is.
I don't know enough about how DOCSIS 3 works or how TWC is pushing the signal to this modem to make a guess as to why it's doing it, but as long as I don't get constant drops, I guess I just have to live with the fact that I can't use pingtest.net to check my line.