Why is my connection not GBE?

[shsesc]

I have an Arris Surfboard 6141 and I run a cat 6 cable to my router across the room. It is an asus rt-ac5300. The modem via a flashing red light and the router info page both show this as less than a gigabit ethernet connction. I don't know why. Why would that be?

 

[failboat]

Test with another cable and check. Cables are very sensitive to how much wire you untwist.

Duplex should be auto on both sides.

Is your internet over 100Mb/s? What kind of results are you getting from speed tests?