That is a DOCSIS 3.0 device. You are not going to get gigabit speeds with it. You need a DOCSIS 3.1 capable modem.
Plus they rate it for a max of 373 Mbps down;
The signal stats are fine BTW.
These are the only approved devices for the gig speed tier currently:
DOCSIS 3.1 Devices
Motorola MB8600 32x8 modem (DOCSIS 3.1)
Arris SB8200 32x8 modem (DOCSIS 3.1)
Netgear CM1000 32x8 modem (DOCSIS 3.1)
Netgear C7800 32x8 gateway (DOCSIS 3.1)