Probably not a valid comparison since I'm in Oklahoma, but I get:
And on Cox's website I get:
Mon May 21 4:29 PM Yes 33 Mbps 8 Mbps 21 millisec (my IP) Oklahoma City
This is with the Arris EMTA modem.. still Docsis 2.0.
I'd start doing Tracert's to various places.. it could be on Cox's local Gateway (node slowly getting over-loaded?) or some router/hop between you and the server. The problem spot is usually the one where the ping time jumps up and that time is carried over to the destination.
What "router" do you have? Have you tried connecting directly to the modem? Have you tried power cycling the "router" ? Sometimes buggy firmware in the "routers" can add latency and cause problems. If power cycling the "router" lowers the latency, I would check for firmware updates or replace the device with a newer model.