need to open ports in my modem

If the problem persists when you are hardwired to your modem, then your ISP needs a talking to. Ask them to open up port 88 for UDP and open up port 3074 for UDP and TCP in their firewalls as well as in the modem. If the modem
has both a USB port as well as an Ethernet port, then it does internal routing and it could be delaying the packets using those ports.

try opening ports on your modem, some games need to have certain ports for better multiplayer performance

Since you are connected by wireless did you configure any ports in yours router/modem management?

Doing port fowarding (opening specific ports) get you a better connection. The alternative is connect by cable, in this case you wont need to open ports.

Is that modem from your isp ? I checked on a few forums and that modem came up "less than friendly" lets say ....I would start with a modem , for me , netgear modem and netgear router was the only thing that got my nat open and KEPT it open....lots of
things will open it , KEEPING it open is the key here.....you never said who/whats your isp either....right modem and router and no need to port forward or dmz or any of that...

Hello nicolatideswell! I'm Claus, an Independent Microsoft Community Consultant for Xbox! Glad to be able to help you!

For your NAT to be set to Open, that will depend on the ports that are currently open on your router/modem. Most of the time, the same device from your ISP will be your router, so you need to call your ISP (Internet Service Provider) and request them to open these ports on their modem/router:

Port 88 (UDP)

Port 3074 (UDP and TCP)

Port 53 (UDP and TCP)

Port 80 (TCP)

Port 500 (UDP)

Port 3544 (UDP)

Port 4500 (UDP)

And to enable UPnP (Universal Plug and Play), you need to enable this setting on the router as well.