Next one is are you using their eMTA, or your own personal modem & router? If you are using the rental equiment (eMTA), then you have two wifi networks. Your private one, and the public Xfinity or Comcast one. Depending on the package you are paying for, you should get good speeds outside of the modem. If the problem is that the wifi is showing all of the time 1 or 5 mb/s when connected to the gateway, something in network settings, or the driver for your device is not up to date.
I only use Wireless-n for all of our devices. I have mine set for 40mhz Channel, Wireless-n only, Channels 1 & 5. If you have some devices that are using wifi and only capable for Wireless-g, you have to leave it at 20mhz Channel, and would be Wireless-g/n, one channel at 54mb/s for g, 150mb/s for n.
When I had Comcast for a short while, I used my own modem, router and Access point. Always got the subscribed speed on the Internet, and had control over my network for wired & wireless devices.
You can use "Shaper Probe" to verify your actual Internet speeds. You can download it at
M-Lab You open a Command window and then run Shaper Probe from the directory it is in. I leave mine on my laptop in the Download directory.