2013 iMac ONLY negotiates 100 Mbps

I have a Late 2013 iMac running High Sierra 10.13.2 that will only negotiate 100 Mbps on the built in ethernet port. It works fine at 100 Mbps. I would use the thunderbolt adapter, but I am using both ports for additional monitors.

Below are my completed trouble shooting steps.

1. Cable. I connected the cable to the same switch port with a thunderbolt adapter and it negotiated 1000 Mbps on my iMac.

2. Switch. I used the same port, cable, and thunderbolt adapter on my MacBook Pro and it too negotiated 1000 Mbps.

Is there any remedy to this nightmare?