Upload speed capped at 40mbps after next-gen upgrade

Following the instructions here to fix my upload speed capped at 40mbps after upgrading to a coda56 modem.  https://forums.xfinity.com/conversations/customer-service/upload-speed-capped-at-40mbps-after-nextgen-upgrade/68402a2a5cfcb01f84c7ee5c

I want to send a DM to xfinity support, but have to make a public post first, so here it is.