Ok so more digging... Well my firmware has 100% been messed with, the screen is obviously different than what it used to be, and now my modem no longer works properly.
What my options screen looked like up until today:
and what it looks like now:
As you can see, there is now a little radio button to select the 5Ghz band, but it doesn't do anything. A soon as I click it, it ticks back to 2.4. I recently got an email about Panoramic Wifi and saw some emails saying that you can manage your settings from the cox website. I wonder if this new firmware was supposed to work with that somehow, but doesn't work obviously?
Just spoke with the Modem Manufacturer's tech support:
Alwin R: Could you please help me with the firmware version?
Me: The firmware Version is D30GW-EAGLE-1.5.3.0-GA-00-NOSH
Alwin R: Kindly contact your ISP & check whether they have updated any firmware recently. If YES, ask them to degrade the firmware.
So.... he's confirming they have the ability to do it, but when I call Cox tech support, they claim they can't, and I have to pay to get this service. Hopefully a Cox Moderator reads this post and can help me out = /
Thanks for responding Jonathan! I did a regular power cycle first, and when that didn't work I did a full factory reset - no change. Interestingly if I go into the main configuration page that lists everything, it does show my 5Ghz network SSID (marked as "disabled"), and when I click the hyperlink to the settings for it, it takes me to the page above that no longer has the 5GHz option available.
I sent an email with the requested info. Thanks again, and please let me know if there is anything else that is required!
After emailing tech support, I received a great deal of help. The conclusion that has been drawn between a Cox engineer and the manufacturer (Arris) is that the firmware is not new, and is in fact a few years old and the interface change was caused by hardware failure (??!?). This seems bizarre to me, but I appreciate them (and everyone here) looking into this strange occurrence. They are going to do a bit more investigating, but unless I report back with another update, case closed.
