Upload speed capped at 40 Mbps.

After starting on a new Gig Speed plan (1100 Mbps download / 300 Mbps upload) and acquiring a new Coda56 modem, I am getting the advertised download speed of approximately 1100 Mbps, but my upload appears to be capped at around 40 Mbps. I have read on this forum about others who have had a similar problem. There were solutions mentioned about re-provisioning the modem or making sure the new modem is listed as Active. Two very long chats with customer service have not changed anything. They are now bringing up the idea of having a tech visit ($$$), but all of my wires are less than 5 years old and signal levels are fine. Xfinity support please advise here.