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
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.