Incorrect Speeds on 1.3 Gbps Plan w/ New Arris S34 - Suspected Incorrect Boot File

Hello,

I'm hoping to get some technical assistance here, as I've exhausted my options with phone/chat support after about 8 hours today. I recently upgraded my modem and I'm not getting my provisioned speeds, and I have a strong suspicion it's a boot file issue.

Here is a detailed summary of my situation:

My Plan & Equipment

• Plan: Gigabit Extra (1200 Mbps advertised, 1300 Mbps with over-provisioning). Upload speed should be 35 Mbps.

• Modem: Brand new Arris SURFboard S34 (DOCSIS 3.1).

• Router: UniFi Dream Machine with a 2.5 Gbps WAN port.

• Connection: The modem's 2.5 Gbps Ethernet port is connected directly to the router's 2.5 Gbps WAN port.

The Core Issue

• Problem: I am consistently getting speeds of approximately 700 Mbps down and 5 Mbps up.

• Measurement: This speed has been verified via the UniFi speed test widget (which measures directly at the router's WAN port) and is consistent across multiple tests.

Troubleshooting Steps I Have Already Taken

1. Isolated the Modem: To completely rule out my internal network, I disconnected the router and connected my laptop (which has a 2.5 Gbps Ethernet port) directly to the Arris S34 modem. Running speed tests in this configuration yielded the exact same results: ~700 Mbps down and ~5 Mbps up. This confirms the speed limitation is happening at the modem or upstream.

2. Contacted Xfinity Support: I have spoken with multiple representatives over the course of 8 hours.

3. Confirmed Signal Levels: Every representative I spoke with confirmed that my signal levels are "excellent" and well within spec (downstream/upstream power, SNR, etc.). There are no correctable/uncorrectable errors being reported by the modem.

4. Multiple "Re-Provisions": Support has re-provisioned my modem at least half a dozen times. Each time, this simply resulted in the modem rebooting and coming back online with the exact same limited speeds. It does not appear that anyone has manually checked or changed the configuration/boot file assigned to my account.

My Request for Help

Based on the symptoms—perfect signal levels, a top-tier modem capable of multi-gig speeds, but a hard cap on both download and upload that is far below my plan's rate—I am almost certain that my modem has been provisioned with an incorrect boot file for a lower speed tier. The ~5 Mbps upload speed is a particularly strong indicator of this.

Could a verified Comcast employee on this subreddit please investigate my account? I need someone to look beyond the basic signal stats and confirm that the correct boot file for the 1200/35 Mbps plan is assigned to my modem's MAC address.

I am happy to provide my account information via Private Message. Thank you in advance for your help.