Instructions

Here are the steps to take the AT&T U-Verse Pace 5168NV DSL Modem you just bought and get it working on Sonic.net VDSL2 internet service.

Download the sonic.net firmware for the Pace 5168NV
Plug your computer into one of the four yellow ethernet ports on the modem and power up the modem
Once you get served an IP address in the 192.168.1.0 network browse to http://192.168.1.254/upgrade
Click Upgrade
Enter the password. This can be found on the label on the modem listed as Device Access Code. This is different from the Wi-Fi Password
Click Choose File and select the pace-5168-10.1.3.500036_reinstall_signed.pkgstream you downloaded above
Click Upgrade. Wait for approximately 5 minutes while the modem installs the patch and reboots.
When the power light goes back to solid green and your DSL/Internet lights come back on, you are ready. You can also tell that the upgrade is complete when your network connection drops then comes back up and you'll get a new IP in the 192.168.42.0 network

Optional additional steps

In my case since I have my own router and don't want to use the router built into the modem first I go to Settings... Broadband... Link Configuration scroll to the bottom and uncheck Routing, then click Save. The password is still the same. When I do this the page then shows and error but it accepts the settings change, not sure why this is.
Next I go to Settings... LAN... DHCP and uncheck DHCP Server Enabled theh click Save. This time I get a green Configuration Successful response
Since I've set the modem to Bridged mode by disabling Routing I don't need to disable the Firewall in Settings... Firewall as it's not in play
Because I have my own wireless access point I then go to Settings... LAN... Wireless and uncheck Enable Wireless Interface then lick Save, just above where it says Wireless Channel