Not getting 'Next Gen' upload speeds on new Arris s34 modem

Hey there, my area was recently upgraded with the next-gen stuff and I ended up needing to get a new modem as my old MB8600 had started having issues with packet loss and wasn't getting the newly advertised 1300mbps download speeds - no problem, the modem was like 6 years old so I didn't mind upgrading.  I did my research and selected the Arris s34 as it supported the 'Next Gen' speed tier on the xfinity compatible device list.

So I purchased and installed my s34 and it immediately resolved my issues with packet loss AND had me getting an average 1250mbps - excellent!  However my upload speed is still stuck around 40mbps.  I've confirmed this running speedtests from my router directly as well as via a laptop plugged directly into the modem with a cat8 ethernet cable. 

I've seen other threads on here with users of the Arris s34 having the same issue which you guys were able to help out with.  Let me know if you need any additional information or if I should send my inquiry elsewhere, I just chose this forum as this isn't urgent and I'd rather handle this asynchronously if possible.