Go into device manager and find your network adapter name. Go to the manufacturers website or the manufacturer of you computer and find the most recent windows 8.1 compatible driver. Or you can right click on your network adapter in device manager and select driver, update, update automatically. Sometimes this method will stir up an update that isn't found using normal windows update methods. But the best method is to find the manufacturer specific updated driver. Also, make sure nothing is annotated or commented in your device manager under network adapters. We've seen a few machines with the Microsoft tunneling adapter showing issues on windows 8.1 machines that are connected to routers which do not support the IPv6 protocol and speeds were an issue.
Yeah, it doesn't look like it. Usually if there is a problem that windows is picking up on there will be a question mark or exclamation point on the item in question. Maybe try the update process outlined.
Update: Actually, go back to the device manager and go up to View and click on Show hidden devices. Now open network adapters and take a screenshot of that and let me see it. Thanks.
Ok, so I don't see any issues there, although you might want to go back in there and right click on each of those listed adapters and then select update driver and update automatically to see if there are maybe updated drivers available that might help resolve the problem on it's own. Do each and every one of those like that. Sometimes doing this will find drivers that Windows update either doesn't see or doesn't check for. If that doesn't help we'll see about updating the drivers manually for the Ethernet controller. After that it's probably something in the router settings or the router itself.
Well, you can do that, but it's doubtful it will resolve a driver or setting issue for network speeds. But you can try it, I've seen crazier stuff work. Let me know if it cures the problem. If not, we'll look some more.