Internet performance over the past several months has significantly declined. When I run multiple external standard speed tests I get HALF the performance of what the xfinity speed test says it is delivering. HALF. I ran many tests from different sites and they are all within a few Mbps of each other. It takes over 30 seconds just to load the xfinity webpage. My home network and PC are already fine tuned - don't tell me to do that. Again, this has really been noticable over the past several months.
Start here: Troubleshooting Guide
If you haven't already, please post your equipment details (make/model of your modem/gateway/router) and a screenshot of your signal levels and your error/event log. Thank you!