Xfinity 2Gig plan with XB8-T gateway does not provide the performance advertised.

I am very unhappy with my new Xfinity internet plan. I upgraded to the 2Gig Plan, which includes the Xfinity provided XB8-T gateway. The gateway has 4 LAN ethernet ports, including a 2.5Gb LAN port. I need to use the gateway in bridge mode to support my existing home firewall and LAN network. The 2.5Gb LAN port on the XB8-T gateway does not provide internet service to a router in bridge mode nor in non-bridge mode. The only way, that I am aware of, to obtain internet service to a personal router in bridge mode is to configure the XB8-T gateway to "Associate Ethernet Port 2 to Xfinity Home Network". Once LAN port 2 is configured, configured, the XB8-T gateway provides internet service to a router in bridge mode. However, LAN port 2 is limited to 1Gb speed, which is half of the speed I am paying for. No doubt this is VERY intentional on the part of Xfinity, to limit data speed to customers. The XB8-T gateway has a 2.5G port that Xfinity is restricting access to in bridge mode.  

Does Xfinity have another gateway available that will provide 2Gb speed in bridge mode, so I can obtain the service level that Xfinity offered and I am paying for?