Not reaching gigabytes internet speed
I am using two cables, a 3m cat5 and a 2m cat5e, to connect between my computer, the router TL-WR1043ND and the modem.
If I connect my computer directly to the modem, I could reach ~800 Mbps for both download and upload speed for both cables. I suppose it means that my network adapter setting, mycables and the networking from the ISP are all fine for providing gigabyte speed.
When the router connected in between, although it is shown the speed will be 1.0 Gbps in the ethernet status, the internet speed drops to 130-140 Mbps for both downloading and uploading as I tested on speedtest.net.
The specification sheet:
https://www.tp-link.com/uk/home-networking/wifi-router/tl-wr1043nd/#specifications
What am I missing here?
Thank you.