Comcast Xfinity is the largest residential ISP in the United States, with cable plans from 75 Mbps to 2 Gbps and a growing multi-gig fibre footprint. Real-world speeds depend heavily on local node congestion and the modem you use.
This is classic node congestion, coaxial cable is shared with your neighbours. Open a ticket and ask Comcast to check node utilisation. Persistent issues can force a node split.
Comcast's xFi gateway is a basic combo unit. Put it in bridge mode and add a Wi-Fi 6 or 6E router (eero, ASUS, TP-Link). Most gigabit Comcast customers see Wi-Fi double after this change.
DOCSIS 3.1 standard upload is intentionally limited. If you need symmetric upload, look for Comcast's new fibre roll-out (X-Class) or an alternative fibre ISP in your block.