I have been using the TP Link AC1350 Wi-Fi Range Extender (AV1300 Powerline Edition/TL-WPA8630 KIT) for many years now with no issues with my ISP providing a maximum 100/100 MBps (which gives me much less in practicality).

Today, I upgraded to GB internet at the router. I've reset my network adapters on the PC. It has GB capability (a Realtek PCIe GbE Family Controller) and I've gone into the settings of the device and chosen the Speed & Duplex value of 1.0 Gbps Full Duplex, checked the cable to make sure it's labeled Cat 5e, and I've upgraded the drivers and still I'm getting much less than a GB.

What additional things do I need to try? I know it's always a "weakest link" thing, but I'm cabled into the TL-PA8010 2.0 device (powerline) with the proper cables. I downloaded the TP link app and when I navigate to the Data Rate, it shows only around 301 Mbps. That's much lower than I'd have hoped BUT I'm still not even approaching that.

There must be something else, but Google always seems to suggest the cables and the settings, which I've checked so I'm not sure what to try next.