What device do you run the speed test on (ethernet device or wifi device)?
What are the download and upload speeds?
How is the xbox connected? What speeds does it get? If it is wifi connected, how far away from the router?
Are you still having this problem?
If you think it might be a routing problem, you could try this.
If you have a Windows or Linux computer or if the xbox can issue commands. If you know the URL or ip address sending the updates, eg.
tracert -d www.xbox.com
will show the path taken by the updates.
You could have your friends do the same and compare. TPG might be going the wrong way somewhere.
You can check the host names by:
ping -a ipaddress
Host names might be informative.
Do you know the website where the xbox update comes from?
If so you can check where delays are in the network.
In Windows, open a command window. Enter the command tracert followed by the website name.
You'll see the path taken and where delays occur. It could be the route chosen by TPG to get to the xbox site.