Gateway issues

I tried the second option as well and my DNS wouldn't resolve the Xbox server names. I've wasted too many hours of my life on this and either way I've had enough trouble with the Arris so we're going to get a new modem. Thanks for the suggestions though.

I have the same issue with the same equipment and the same ISP. TW will put your gateway in bridge mode by just calling them. The best work around Ive found until I can get a new router and use the Arris garbage is bridge mode is this... Start your game,
go to multiplayer... If it won't connect press the guide button while game is still running, go to settings, network, test connect then test multiplayer connection... while on that screen, hold down the R&L triggers and bumpers and wait for the NAT mode to
pop up. It should be open. Then just go back into your game and play multiplayer. So far this has been working for me and my NAT is open.

This is all assuming you have UPnP enabled and the firewall disabled.

Hope this helps.

Just Rebooted both the gateway and my router and now I am getting a strict NAT but the error code only says I'm behind a Port Symmetric NAT. I suppose that's some progress haha

There is some indication that a TW tech can put the Arris in bridge mode or that you can do it yourself by logging in immediately after resetting it to defaults:

www.dslreports.com/.../r27274883-TWC-Does-anyone-else-have-an-Arris-DG860a-modem-

Alternatively, see if TW will provide a modem only or buy your own (cheaper than leasing in long run and gives you more control). Failing that, assuming you can configure port forwarding, DMZ, etc. on the Arris, you have a couple options. First, with the
Arris connected to the WAN port of the N900, you could try putting the WAN IP of your N900 (this should be a private IP received from the Arris over DHCP) in the DMZ on the Arris (delete any other forwards on the Arris). Do all port forwarding and DHCP as
usual on the N900. Or, second, you should be able to use the N900 as just a switch + wireless access point (bypass NAT routing) by disabling DHCP on the N900 and connecting the Arris to a LAN port on the N900 rather than to the WAN port. All NAT, port forwarding,
and DHCP would then be provided by the Arris.

Personally, I would just get a modem only, such as the Motorola 6141 (if supported by TW).

Sounds like both the Arris and E900 by default use a LAN IP of 192.168.1.1. You will need to change the LAN IP of one or the other from 192.168.1.1 to 192.168.1.X (where X makes an unused IP outside the range that the Arris is configured to hand out via
DHCP). To change it on the E900, you will probably need to temporarily unplug the Arris. You may have to set your PC to a static IP of 192.168.1.X to reach the E900 but try without first.