Very slow upload speed

My problem seems identical to the one described in this post: https://forums.xfinity.com/t5/Your-Home-Network/Extremely-slow-upload-speeds/td-p/3059871

 

I have the 300/25 service. My only issue is that the upload speed is consistently <40% of what is advertised; consistently in the 6-8 Mbps range when I typically use the internet. It's 10am on a workday, when I'd normally be at work, and I'm seeing 11 Mbps for the first time ever; reported by Speedtest.Xfinity.com and Fast.com. This is a real problem, as I want to stream video with my calls to friends and family in the evenings but ~7Mbps is a bottleneck. I recently upgraded form the XB3 (TG1682G) modem/router to a Netgear CM1150V for other reasons and the upload issue persists.