Does the modem feel very hot when it’s running? I’m having a very similar problem with my G34 and I have temporarily resolved the issue by pointing a fan directly at the modem. I went from disconnecting every 20 minutes or so to having no issues whatsoever. I’m waiting to hear back from customer support about how to resolve this.

It doesn’t feel very hot. It even goes down in the middle of the night when everyone is sleeping. 

I have this exact same issue! I got my router in February on Amazon, so I’m outside of the return window. It worked fine for months and now it’s dropping the connection daily, multiple times a day. It’ll work after being reset, but then it’ll go out again overnight. I work from home & need a reliable internet connection! We’ve had 3 techs from Comcast come out & they’ve confirmed that it is not an internet signal issue. It’s fully on our end. They think an update might be necessary. 
 

From other comments I’ve seen, there may have been an update back in November, but I don’t know how to access it. I don’t want to spend another $300 on something - I want this one to work or get a replacement!

Since you are experiencing intermittent internet connection, I would suggest changing the Wi-Fi channels if the issue is with the wireless connection.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Changing-the-Wi-Fi-Channel

If you are experiencing both wired and wireless connections, I would suggest checking the cable signal levels.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Cable-Signal-Levels