We recently upgraded our AT&T fiber internet to 300up/300down, which required a new modem. Before the swap, my particular computer was getting about 80mbps down, 10mbps up. After the swap, my down speed is capped at 5 mbps, but my up is 100 mbps (we still need to upgrade our switch to a gigabit switch).

I've tried every setting I can find as well as uninstalling and reinstalling the network adapter.

I plugged my network cable into a laptop just to confirm that there are no hardware problems between me and the switch, and the laptop got full up and down speed, so there's definitely something on my computer that's capping my speed.

Computer is running Windows 10 Pro and is on a domain network. All other computers on the same network (All Win7Pro or Win10Pro) have full up and down speed. Mine is the only one suffering this download capping issue.

Network adapter is Realtek PCIe GBE Family Controller. Tried updating driver. No joy. Connecting same computer via wifi gets 35mbps down, so the cap is adapter specific.

Down speed this morning was 85 mbps. Provider was AT&T and still is. They did swap out the modem for one that could handle the higher speeds, so modem is new.

Also already disabled Windows Auto Tuning via cmd prompt.

Any insight would be super helpful.

Current speedtest.net results:

PING ms 1 DOWNLOAD Mbps 5.51 UPLOAD Mbps 286.07

I connected directly to the modem to see if it's a switch issue, but even with the switch out of the equation, I'm capped at 5 down.

Also attempted Windows Network Reset. No improvement.

Bootable USB running Ubuntu using same machine and adapter is able to access full 300 download speed.

UPDATE: After booting Ubuntu, confirming speed, then restarting into Windows, suddenly my speed is up to over 100 down again. So basically I just had to make windows feel threatened that I was going to leave it for another OS? ¯_(ツ)_/¯

  • What was your prior speed? Was it with another company and different modem? – Eric F Dec 5 at 21:09
  • Down speed this morning was 85 mbps. Provider was AT&T and still is. They did swap out the modem for one that could handle the higher speeds, so modem is new. Also already disabled Windows Auto Tuning via cmd prompt. – Jenna Ali Dec 5 at 21:14
  • Could you try using one of the live Linux operating systems. Ubuntu desktop has a browser included. – chew socks Dec 5 at 22:45
  • tutorials.ubuntu.com/tutorial/… explains how to create a LiveUSB which will boot Linux from the USB without altering anything in Windows. – K7AAY Dec 5 at 23:06
  • @chewsocks I did that an Ubuntu was able to use the same adapter and access full speeds, no problem. So something weird is happening in Windows. I just can't figure out what it is. – Jenna Ali Dec 6 at 0:08

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