Troubleshooting slow speed, identified high upstream transmit power

I'm subscribed to 1,200 Mbps internet service, but my Netgear CAX30 is consistently getting approximately 400–425 Mbps download on the Ookla Windows desktop app over gigabit Ethernet.
I've factory-reset the gateway, confirmed Traffic Meter is disabled, tested multiple servers, and checked the coaxial connection.
Please verify that my modem has the correct provisioning configuration/boot file for my subscribed speed tier. My modem also reports upstream transmit power around 53–54 dBmV, so I'd like the line signal checked.
I'm hoping to have the service configuration and signal levels investigated before equipment replacement is recommended.