DOCSIS3.1 Motorola MB6811 swapped for Xfinity modem and now speeds are capped

I recently put in service my own Motorola MB8611 which is on the list of approved modems for my plan.  As soon as I connected it and checked the connectino speed on a wired desktop I showed a maximum of 720Mbps Down and 5.71Mbps up. On the previous day I got 900Mbps down / 240Mbps up on the Xfinity modem. Two hours using chat trying to troubleshoot, 90% of the time with some automated canned messages about how my issue was the top priority and the same questions being asked and the answer was, the problem is with my equipment. I shouldn't be surprised to get inferior service when you bring your own device which has the same capabilities as theirs.  Has anyone gotten the internet speeds they are supposed to get with their own equipment?