Windows 10: Why have my Mbps download and Mbps upload gone down by so much?

I am a pc gamer, and have built my own pc. starting from yesterday night, my ping has went up by a lot and Mbps download and Mbps upload gone down by so much; i don't know whats happening. I've tried restarting my router, but that wasn't the problem. ive gone from 800 all the way to 50 mbps

:)

 

Mbps download at 255.8 but Mbps upload at 0.35,

this happens at random times. usually the mbps upload speed is around 10 or 11 but then suddenly it just turns to sub 1. im using windows 10 pro, i use cox wifi 5g. this is only a problem with my pc since any other device has higher upload speeds when this happens

 

Curious about the difference beteen G5 mbps and the 2.4 mbps network

On one PC I get on the G5, 75 mbps download and 8.6 mbps on the upload and ping 114 ms (speed test)
On the other PC with 2.4 mbps I get on average 16.8 download and 4.6 upload and ping 21 ms (speed test)
Yet the speed between the 2 PC's does not seem to be that much different when browsing.
Furthermore, I tried to get the second PC also on the G5 but for some reason the G5 does not come up on the network list.
I was told that being on the G5 you get less interference using Wi-Fi.
Both PC's have the windows 10 OS.
I did reset the modem and I reset the network, but it did not make the G5 come up on the network list of the second PC, whereas before I changed mine to the G5 from the 2.4 you could see that both were visible on the both PC's network list.

 

Mbps

How do I find the Mbps for my particular system?