A few days ago I noticed that my Internet speed was noticeably slower. Called Cox and they said it looked fine. I then dragged over my laptop and connected it to the router using a CAT5 cable same as my desktop. Internet speed was excellent on the laptop but miserable on the desktop.
Did a bit of digging on the desktop. My new Dell PC had performed a couple of updates. I checked into the network interface on the Dell and found it is using an Intel chip on the motherboard for Ethernet / Wi-Fi. Don't care about Wi-Fi cuz I am hard wired to the router. There is an application on the Dell called, "Killer Control Center" which manages various options for the Internet connection such as application prioritzation, auto bandwidth and other useless stuff. Discovered that If I turn off all the "automatic" stuff and prioritization, that the Internet connection improved dramatically. Decided to go to the next step and purchased an Ethernet card off Amazon for about $25. Installed that bad boy in the Dell desktop and wow ... what a difference. I have Cox fibre and now my Internet speed at noon today is 700Mbps download and 725 Mbps upload. During off-peak even better.
If your PC has the Ethernet on the motherboard and you are using a CAT5/CAT6 connection to the router, consider getting a dedicated NIC ... you might see a dramatic improvement.