It may just be your modem, or someone uncapping their modem in your area. Check what speed you should be getting, then verify it with a internet speed site like dsl-speeds. If there is a big difference contact your cable provider. If there isn't, the problem lies with your xbox. Since you cannot call support because you opened your xbox, check to see if your modem/router has a NAT setting. Make sure it is open, and not on strict or closed, as this can limit your connection. If this dose not work, check under the xbox connection screen for the speed at witch your xbox is connecting at. Check the cable feed from the 360, it may be a damaged/kink in the wire, sometimes the stooped things are the easiest to overlook.
Also your xbox live gold account trial should not have any limitations.
This post has been edited by Jonolche: Dec 8 2006, 11:18 PM