My internet upload speed over an ethernet connection is seemingly being throttled - how do I track down the cause?

[John G. 20230209]

My internet upload speed is seemingly being throttled when I'm wired-in over ethernet. When I run a speed test, I'm getting results in the neighborhood of ~90Mbps Down/0.2Mbps Up over fiber.If I'm connected to the Wi-Fi from the same router, I'm getting more normal numbers (~50Mbps Down/~50 Mbps Up).When I do a safe boot with Network, my upload speed over ethernet is also closer to what I would expect (~90Mbs Up). Given these items, I've eliminated anything outside of my computer as the issue, so I'm thinking there must be something running on a normal boot which is causing this - some program

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