Major Drop In Internet Speeds - Please Help

I went from ~400 Megabits per second to ~5. I'm pulling my hair out. My ISP is WOW (Wide Open West) of course there is nothing on their end, no outages, no help offered. I have reset both my modem and router several times.
The only thing that has changed recently was me updating Windows 10 (I didn't notice any internet issues after downloading the updates though.. but now a few days later I'm really worried with these speeds).
I currently have the TP-LINK AC1900 Router and the Netgear CM600 Modem I have never "updated drivers" or "checked firmware" etc etc on these devices. Nor on my computer. Seeing as how I've never done it I'm at a loss and would greatly appreciate any information and tips you can offer along with HOW to "check the drivers on your router" etc.
I'm running Windows 10 Version 1909 (OS Build 18363.778)
Again, I really appreciate any help you're able to offer. I'm at a total loss here, and as you can imagine 5 Megabits/second is virtually nothing and my house cannot operate off of it.

 

go to gpedit.msc (Group policy Editor) then follow these instructions. Under computer configuration - administrative templates -network - QoS packet Scheduler. Then go to limit reservable bandwidth and chang it to enabled and in the bandwidth limit change it 0 and that should improve your speeds on windows 10.

 

I appreciate it, I tried it and no change

I'm finding that after rebooting my PC or power cycling the modem/router it will greatly increase speeds... for about 5min

 

Sounds like your ISP is throttling you.