High ping spikes and sub-standard speeds.

I've been experiencing frequent ping spikes for the past few months of around 600ms with the longest lasting up to 12 seconds. I've determined that the problem is not between my network card and my router as when I ping it, I get a consistent 2 or 3 ms. The router is a relatively new Linksys EA8500 with a Netgear CM1000. Any ideas of what it could be? The cox service people just say that it's fine every time, but it's been consistently unusable especially with high packet loss.

Anything will help, I'm pretty desperate at this point as there are no other providers in my area.