What ISP Service do you have? Cable or DSL?
What ISP Modem do you have? Stand alone or built in router?
What wireless modes are you using? Mixed?
I would set up DHCP Reserved IP addresses for each device connected to the router, both wired and wireless.
Do this under Setup/Networking. This will ensure each device gets it's own IP address and does not conflict, easy to manage and helps to troubleshoot if needed.
Ensure each device is set up for Auto-Obtain IP addressing.
Review the DGL-4500 forum sticky for gameing and gamefuel settings for xbox. The UI is different however the data contain will work for prioritizing and QoS for xbox and other devices.