Ok, keyboard commandos, I have an issue and I need some assistance. I have Cox internet (I live on post) and have the "Internet Preferred" service that says "up to 100mbps" download speed.  I am running a Linksys WRT 1900 AC router, with an Arris SB6183 cable modem. My desktop connects to the router via a USB dongle plugged into a USB 3.0 port, and connects to the 5GH band on the router.

On Friday, my PC crashed, and I ended up having to replace the C drive with a new SSD and do a complete reload of Windows 10. Prior to this, the internet on my desktop worked fine. It was fast. Web pages loaded almost immediately. I downloaded a 1GB zip file from my school's website in less than an hour. Unfortunately, since I inadvertently wiped my D:/ drive in the process of trying to fix my desktop (DISKPART is dangerous, lol), I have to download the file again.

Now, both Firefox and Edge are saying that it will take more then 10 hours to download the file at a whopping speed of between 15-25 Kbps. WTF, over?

At first, I thought it was because OneDrive was downloading and syncing around 9GB of files, but I left the computer running overnight and that is now finished.

Due to the positioning of the computer to the location of the router, running an Ethernet cable is difficult, and connecting wirelessly is my only option.

FWIW, my Xbox also connects wirelessly, and I am able to play games and stream Netflix on it just fine. (Obviously, I do not have that on while I am trying to download this troublesome file.)

When I run a speed test, I get this: Ping<T1 ms, Download 1.64 Mbps Upload 19.83 Mbps

UPDATE: Well, my new PCI WiFI card came from Amazon today, and it was the USB dongle that was causing the issue. I installed it, let Windows find and install the device driver, and it works splendidly. The speed test gave me this as a result: Ping<1 ms, Download: 66.35 Mbps, Upload: 33.22 Mbps, which is much more in line with what I am paying for.

my wag is drivers
can you try a wired connection right to the router?

make sure the mobo/network/ect drivers are all up to date, get them from manufacturer websites

If you haven't already, start with the simple stuff.
Power everything off. Power cable modem on, then router, then PC.
If not fixed, temporary run an Ethernet cable, disable wifi on the PC and test speed.

Try a speed test on the Xbox, I think you can do it in settings where you setup your network connection.

Try a speed test and see what it shows. It's possible it's a driver issue but it's also possible that the issue is on their end and the connection is being throttled for whatever reason.

Well, I downloaded all of my drivers for the motherboard, which seemed to help. I ran the speed sets (again) and it is a little faster.

Ping<15 ms; Download 0.77 Mbps; Upload 5.55 Mbps.

I tried the file again, and it still says 9 hours. For comparison, I downloaded the file from my wife's laptop and it took 15 minutes. I am still thinking it is something in the hardware/BIOS/drivers or the USB WiFi dongle. I ordered a PCI WiFi card, which should be here tomorrow, and I hope that it fixes the issue.

no option to run a wire for testing?

15 min vs 9 hours? about 40x diff

i would wager usb driver

v1.x 12mbps
v2 is 480 mbs

a factor of @ 40

v3 is 5 gbps

I can run a wire for testing, but I have to find it first. In a box of computer stuff. In the attic.