Slow internet speeds on one device

I have Gigabit service at my home office and noticed degradation on one of my desktop PC's.  Sitting next to each other, two identical Dell machines, one gets 885 down/ 42 up, the second troubled machine gets 46 down/ 42 up.  Here is a list of steps I have taken so far with no fix.

Reboot Comcast Gateway

Reboot PC

Changed the ethernet connection on the gateway to a blank port

Swap ethernet cables between good and failing machines

Download and apply new device driver for ethernet NIC

Shutdown firewall and AV

Update FireFox and Chrome

Run Microsoft and Dell diagnostics

Changed the IP from DHCP to static

Manually changed the DNS servers to 8.8.8.8., 4.4.4.4

Only thing I have not changed is the MAC in the NIC.  I even took a laptop and used the ethernet cable from the failing machine and it got full speeds. 

What is going on?  Any help is much appreciated.