Dell Precision 390, Suddenly Very Slow Upstream

My web server, a Dell Precision 390, normally tests at about 50-60mbs down and 11mbs upstream.
Today, it's testing at only 0.8mbs upstream speeds.

No one touches this server--it's configuration is static and it's been very reliable til now.

The O/S is Windows 7 Pro 64-bit. The network adapter is shown as "Broadcom NetXtreme 57xx Gigabit Controller" in Network properties.

I've rebooted the server and the modem and the router it's connected to, but it continues to be pokey on upstream. Other PCs on the same node are seeing about 11.2mbs upstream.

Has the network interface simply worn out?

Welcome to the forum If your using speedtest or similar select another server often it will test against a distant server which will give that type of results. You also need to check the server isnt having its disk hammered or a lot of network traffic a windows update can cause it as well

I've tested against the closest server and can reliably replicate slow results on the Dell and faster results on other PCs on the same router.

The Dell used to test faster, but I think something has worn out or simply broken in the past week, as it is running at 8% of the usual upstream. The odd thing is it surges to 11mbs at the start of the upstream test, then it degrades rapidly to a very low number. The test takes several minutes to complete on the Dell, where as it takes only seconds on other PCs connected to that router.

Did you check disk and CPU usage when running test as speed test writes to be it will be slow if there is heavy usage. Is it normal copying files on the own if that's ok nothing wrong with network card

Peaked CPU usage around 60% during the test, settled back to 0% when test completed.
No changes to configuration on this machine since 2015 when it was set up and finalized.
I just did a file copy operation across the LAN from a disc on the server to my local Win 10 PC's SSD drive. Task Manager showed Ethernet Receive rate of 90 Mbps. So the hardware is evidently okay.
Just internet upstream is slow on that PC.

How is it connect ie straight the router or via a switch if you have a modem what speed direct to the modem

So many speed test often choose a server a long way away resulting in slow speed

I know that, but this test CONSISTENTLY runs on my other PCs and is only slow on on upstream test on the Dell 390. I also manually choose the closest server to me.
I think the software that runs in the browser is the issue. To get 0.8mbs on Speakeasy and 11.2mbs on Ookla, where other machines test at 11+ on both, tells me there is some incompatibility between Speakeasy's current application and the browser on the Dell machine.