I am in Central actually myself. I feel your pain, I really do. Nothing seems to change it though and nothing seems to push cox to show they even really care. They know we have no other options and really abuse that fact. I would definitely encourage you to file an FCC complaint and start documenting the times they drop UP speeds. If enough of us file complaints then they will be forced to do something.
When they give me reasons why this happens its all standard cookie cutter answers. If the service was messed up by a bad line or my equipment then I wouldn't ever get the speeds I pay for. It just wouldn't work at all, period. You can definitely see that during high traffic hours they limit the up speeds, as well as the down speeds, to as little as legally possible.