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To me it seems like a file sharing application (e.g. BitTorrent based) may be hogging the uplink. Bring up the Windows Task Manager (Shift + Ctrl + ESC), go into the Performance tab and then go into Ethernet or WiFi on the left, depending on how you're connected. If the "Send" value shows continuous activity, go into the Process tab, then click the Network heading (indicated below) to sort down by network usage. This should reveal the culprit. In the following example, I ran an upload test in Firefox, so it clearly stands out here: If nothing shows up on your computer, try disconnecting every network device you have (mobiles, tablets, Internet connected set top boxes, etc.) and rerun the upload speed test on your PC. If the upload speed is much better, reconnect a device, wait a few minutes and rerun the upload test. Repeat for each device.