It should not behave like that. If you have not modified the setup (eg. by adding your own router), there should not be a slowdown as you describe. Give Telus tech support a call, and they should be able to do some troubleshooting from their end.
Are any of your devices connected to wireless on the AP that is used for the wireless boxes? If yes, that could explain it. Ensure you're connecting to the main wireless network SSID.