Gigabit speeds not working through Thunderbolt to Ethernet Adapter

Macbook Pro model 13,3 running Mojave 10.14.1 Darwin Kernel Version 18.2.0 connecting to ethernet using an Elgato 3 Thunderbolt dock. I already know the rest of the network infrastructure is fine and I can get Gigabit speeds via Wi-Fi on the laptop. The problem is that when connecting to ethernet via the Elgato dock the connection will only work if it is limited to 100TX. If I try to manually change the network connection to 1000baseT the adapter never "comes online", "connects", "goes from red to green", etc etc whatever you want to call it. It doesn't work, MacOS acts like it isn't plugged in.

I've been on the horn with Elgato support and they can't figure it out either. My coworker has the same model Macbook Pro and the same model Elgato 3 Dock and he gets gigabit just fine through it. The only difference is that he did not upgrade to Mojave.

Here's what I've tried so far, with no luck (These were instructions from Elgato):

1) Install the TB3D Utility. If it is installed, uninstall and then reinstall it. It can be found here: https://help.elgato.com/customer/en/portal/articles/2663912-how-do-i-install-the -thunderbolt%E2%84%A2-3-dock-utility-?b_id=360

2) Perform PRAM/SMC resets. Please review these articles before doing so: SMC reset: https://support.apple.com/en-us/HT201295 PRAM/NVRAM reset: https://support.apple.com/en-us/HT204063

3) Create a new location: - Connect the Elgato Thunderbolt™ 3 Dock to the Mac. - Connect the Ethernet cable to the port on the Elgato Thunderbolt™ 3 Dock. - Go to the Apple menu, and choose System Preferences.... - Select the Network section. - Select "Edit Locations…" from the Locations menu. - Add a new Location, name it as you please, and then click Done - Click the Apply button at the lower right edge of the Network preference pane. - At this point, all the possible network interfaces that exist on your Mac are visible, including the Ethernet port of the Elgato Thunderbolt™ 3 Dock, which is labeled "Thunderbolt Ethernet Slot", along with a number - You may need to wait for up to 20 seconds before the red indicator to the left of "Thunderbolt Ethernet Slot 1, Port 2" changes to green.

4) Adjust the Duplex Option: - Unplug the Ethernet cable from your Elgato Thunderbolt™ 3 Dock - Go to the Apple menu, and choose System Preferences.... - Select the Network section - Select the Thunderbolt Ethernet Slot associated with the Elgato Thunderbolt™ 3 Dock - Press the "Advanced..." button, then press the "Hardware" tab. - Set Configure to "Manual", and select the speed of your router, like 100BaseTX - For Duplex, choose "full-duplex" only. Do not choose the "energy-efficient-ethernet" option. Keep the MTU setting as the default, like Standard (1500) - Press the "OK" button. - Press the "Apply" button. - Plug in the Ethernet cable into Elgato Thunderbolt™ 3 Dock