Xfinity network is very slow, any thoughts?

I live in Lakemount Issaquah, my network is slow...  testing speed, it is between 10Mbps - 70Mbps most of the time, sometimes it can reach ~140Mbps, way less than my plan 1000Mbps... Also, the network is not stable, xfinity support personal came and checked the cable connections, no problem there. I restarted modem, router many many times... so frustrated... 

What competitor's service are you using?