Speed reduced after switching to CODA56 modem

I switched from xFi gateway device that was included in my plan to my own CODA 56 modem. The download and upload speeds went down after the switch. I already contacted customer service and got the device added to the plan but the speeds are still slow.
With xFi I was consistently getting ~950Mbps download and above 100Mbps upload. With new modem, the speeds are consistently down to 60-700Mbps down and 40-50Mbps upload.

I've read many posts here mentioning XFinity sending firmware update and a "strong signal" to correctly set the channels. I'm lost, however, on where to ask for this "strong signal". So far I've tried restart my modem multiple times, waiting overnight, but the speed is still slow.

I'm using my own wifi router that is connected to the modem over 2.5Gb port. The same setup with xFi in bridge mode gives higher speeds, removing the possibility of line interference.  

I see 32 ports connected for downstream and 4 ports for upstream with my modem, though out of 2 OFDMA Upstream channels, one is marked as disabled.