N900 Dual Band Modem/Router

I just upgraded my Modem to a Netgear N900 Dual Band Modem/Router.  Everything was working great for a day, then we suddenly lost the capability to have both bands on at the same time.  Using the wifi button, I can cycle between the following:  wifi off, 5g on, 5g and 2.4g on - this is where the 5g cuts out after a second.  I can have one band on, but not both at the same time.

Unless someone has a suggestion, besides recycling the modem (done twice), I'll be heading back to the Cox store tomorrow.