Question Recently built gaming rig but can't get past 100mbps


May 3, 2018
So a few months ago i had built a gaming rig but for some reason i cannot get up to the internet speeds that i am paying for. An older, pre-built computer has no problem getting to the 250mbps range. I have all computers connected through ethernet and have confirmed it is not the cables nor the modems/switch/router. Its not hindering me but i really want to know why this is.

Computer Specs:
i5-9600k CPU
Phantom Gaming 4 Motherboard
has an ssd, 16gb ram and a rx580 gpu.

I have also gone through and checked my modem/router settings and could not find any indication why there is a bottleneck. Any help would be greatly appreciated.
There is not much on the computer. It is highly unlikely it is something like drivers because the speed negotiation is mostly done by hardware and this methodology has been set to many years so its not like its new code.

Check to be sure you have the port speed set to auto. The router is on auto and likely can not be changed and if one side is auto and the other is not you get random results at times.

It almost has to be the cable at least you really hope because other than that you are talking a defective ethernet port in your new motherboard.

Cables are really strange when they are bad. They can work in some machines and not others. There is massive amounts of fake cable on the market. You want to be sure you have cat5e or better (don't spend extra for cat6 or cat7). The cable must be pure copper no cca. The wire size needs to be 22-24, no flat or thin cable.

If you are using any in wall cabling check with your machine plugged in directly to the router it is very common for the wall jacks to get loose wires over time.