Pete,

I doubt that it is because of the switch over to xFinity. They just switched up here and I'm running at

14 Ping
21 Mbps Download
4.3 Mbps Up

When my service is slow, it usually is the result of someone backing into the cable box on the street. Sounds like you need a service call.

Also, xFinity has competition in our county, AT&T fiber optic. Every time xFinity (Comcast) attempted to raise my fees, I initiate discontinuing the service. They have an entire department trained to intercept the request and try to keep the customer. Every time, they have lowered their fee to match AT&T.