Head over to thinkbroadband.com and register and then click on their Tools link on the left hand frame.
Set up a BQM (Broadband Quality Monitor) and link the live graph here. Undoubtedly you'll be asked by VM to do this anyway, so forewarned is forearmed.
You'll need to wait a couple of hours to get any meaningful data on the graph but I suspect you are also suffering the same issue that many here are, that being high packet loss on your connection which will cause no end of rubberbanding, lag and ultimately disconnections.
Sorry to hear about the trouble you're having when playing with your Xbox. Are you using a wireless or hard-wired connection? I've taken a look from our end and everything appears normal at first look, but please do get back to us so we can continue to investigate.
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