Upload Speed

I recently signed up for an Xfinity xFi internet plan (1gbps) and while the download speeds are largely exceptional, I have been having trouble getting good upload speeds.

I'm using an Xfinity-supplied modem (XB8). I'm also using a direct ethernet connection to my gaming device (cat6 eternet cord, going directly to a Playstation 5 from the modem; not using wifi at all for uploading). My area is confirmed to have upload speeds of 100 mbps available (even though my plan supports 300 mbps), but I'm not even getting half of that.

The upload speeds vary, depending on the time of day. In the middle of the day, I'm getting anywhere between 33.4 and 40.3 mbps. During the night, it's 7.7 to 19.9 (average being about 15) mbps. I have dozens of photos from connection tests.

I'm very disappointed in these results. What can be done to increase these upload speeds?