My guess is the 2.4Ghz signal is congested in your area. Maybe someone got a repeater or different router and is using up more wireless bandwidth. See here for instructions on how to scan the networks surrounding you. You want to find the 2.4Ghz channel that is least congested, choosing between 1, 6, and 11. The problem is I don't think the Panoramic gateway allows you to specify wifi channels, as per here. I think the theory being all gateways on channel auto-scan would mean they could work around each other, each changing channel as the situation changed. I don't think it works well in practice though.
As for what does work well, you have have a few options. If you get the gateway for free then bridging and buying your own router is one option. If you have Cox phone service, then swapping the gateway for a eMTA(TM3402) is a better option. If neither of those apply, then buying your own modem and router is best.
