I have recently upgraded my internet to a faster connection 1000Mbps download and 50Mbps upload.

In the routers buildin speedtest it is testing the speed to around 500Mbps download and 45Mpbs upload.
On my computers i can succeed getting my speed up to 300Mbps download and 40Mbps upload on some servers using my ISPs speedtest (ziggo speedtest) or fast.com i can get it a bit higher still not enough. When I connect to the cable directly to the ISP modem i get a much higher speed around 800-900Mpbs

I have already tried to log into the web interface of the C5400 and go to Advanced->QoS, manually set the speed to that you get from your ISP, and leave QoS on Standard, then reboot the router and confirm the speed again. But then I still do not get the speed I get from the ISP.

I have also tried a factory reset, but that does not help either.

Any other suggestions to improve the speed?