Steam download speed is good for the first cupple of seconds then it drops and stays down

going take a lot longer than 20 hours, the download rate dropped to 0. did you check your drive space?

I had an interesting experience the other day that may relate to what’s happening with that DL speed drop.
But first, are you using any vpn while downloading? Have you access to a good quality vpn service?
I was uploading a 1.2GB avi file to my cloud storage google) with my service being 50down/10up and it was saw-toothing every few seconds between full 10Mbit/s up falling quiclky to about 1or 2 Mbps, then jump to 10Mbps etc etc.
WTF so I thought to try with my PIA vpn connected and voila full speed 10Mbps upload all the way.
I’m convinced my isp was throttling that upload for some criteria identifiable in the avi file, that they couldn’t identify with the VPN encrypted tunnel.
VPN while downloading if you can, may fix this.

Try changing download region

Your internet provider is doing traffic shaping [https://en.wikipedia.org/wiki/Traffic_shaping](https://en.wikipedia.org/wiki/Traffic_shaping)

That’s how the can offer gigabit internet speed to so many customers and be so massively oversubscribed, yet still pass speedtest tests.

Try pausing and resuming it. I found the client handle very bad network issues like sort disconnections.