1Gpbs symmetrical service capped at ~500Mpbs upload

Hello Comcast/Xfinity Support,

I’m on the 1 Gbps symmetrical Internet plan. My download speeds consistently exceed expectations (1.2 Gbps), but my upload speeds are stuck at 40-50% of this, regardless of time of day.

This used to work for weeks at a time and fixed itself after a modem restart. No longer. I have ruled out local equipment and configuration issues. 

Could you confirm the following:
- The upstream service profile I am currently provisioned with?
- Whether my Vantiva CGM601TCOM modem is fully provisioned for symmetrical multi-gig service on your network?

Tech visits have been unsuccessful. Interestingly, the last one swapped my modem for a new one. This worked for a few days before reverting to the lower speed above i.e. as if the modem once again updated itself to a downgraded speed. 

If additional testing or information is needed from my side, I am happy to provide it.