Hi BusinessBill,
Welcome to Microsoft Community.
This question seems strange. Have you installed any updates on your computer recently? At this time we have received no known issues with inconsistent disk transfer speeds.
About how the hardware behaves in Windows,
The best place to get help with hardware performance is Microsoft Learn(English only), which aims to support more advanced users like you.
Here is a link to the forum where you can raise specific scenarios and share your idea to help solve the problem.
I won't be able to help you, but I'll leave that question open in case one of our amazing volunteers has ideas for you.
Thank you for your understanding and patience!
Best Regards,
Manson - MSFT | Microsoft Community Support Specialist