chromebook

I have a1GB Xfinity speed connection, and an Xfinity Gateway Modem/Router, and I use a Chromebook.   When I run Xfinity Speed Test, I consistently get 22 Mbps speed.  I have tried all the various suggestions I have found online.  I can connect to the Internet, and the response time feels decent, why is the Xfinity Speed Test not showing me at least 700-800 Mbps? I have a Samsung Tablet and it does show high speed connections, so I know my Internet connection is good. 

I read that this may be a problem with IPV6?  Did Xfinity make a change to my Network?  Thanks.