Gigabit x2 plan - Motorola MB8611 Docsis 3.1

Hi all, 

I have the Gigabit x2 plan, yet when I bring up my account, it states I have download speeds up to 1.3 gbps. I have a Motorola MB8611 modem. Is this modem capping my speed? The modem is supposed to be able to handle speeds up to 2.5 gbps. I am wondering if this modem is not allowing me to reach the full potential of my plan. Thanks