The modem and router are 2 different devices but Cox can lump them into 1 for a rental fee. The modem side of your device is probably okay but it's the router side being awful. Panoramic is not a good router.
Do you need gigabit service or did you get by okay with your previous data plan? If you were satisfied with your previous plan, bring it back. Return the Panoramic to eliminate its rental fee, cancel your gigabit plan, restore your previous plan, reconnect your previous modem and purchase your own router.