Sort of the same problem…swapping out two PCIe network adapter cards wouldn’t give me above ca. 500mbps down on my Win10 Pro desktop, even though my laptop managed ca. 925 on a 800 plan. Finally bought and installed a TP-Link 10/100/1000 PCIe card, and - presto!, got my speed. Can’t explain why, but couldn’t argue with the result.

I have a 50ft homerun of RG6 Quad coax from demarc > modem giving excellent ping, download speed, and power stats since I installed it. Proper cable and attention to F-type fitting attachment will give trouble-free performance.