Welcome!What Hardware version is your router? Look at sticker under router.
What
Firmware version is currently loaded? Found on routers web page under status.
What region are you located?
DMZ only allows for one device IP address to be used.
I belive you have the latest version if you have a Rev B router.
Does your router settings have a QoS option under Advanced with some rule entries listed? Or just QoS enable or disable?
What ISP Modem make and model do you have?
Some things to try:
Turn off ALL QoS or Disable Traffic Shaping (DIR only) GameFuel (DGL only and if ON.) options. Advanced/QoS or Gamefuel.
Turn off Advanced DNS Services if you have this option under Setup/Internet/Manual.
Turn on DNS Relay under Setup/Networking.
Setup DHCP reserved IP addresses for all devices ON the router. Setup/Networking
Ensure devices are set to auto obtain an IP address.
Set Firewall settings to Endpoint Independent for TCP and UDP under Advanced/Firewall.
Enable uPnP and Multi-cast Streaming under Advanced/Networking.