i had a similar issue once. a component was getting too much power or not enough and it was heating up some wires. idk if it was shorting or what but replaced the device and the smell went away
the gpu was factory oc or you oc?
I've fixed issues like that by switching hard drives or reinstalling windows. i had a similar issue to that once but it was my gpu throttle to keep the fan quiet
latest nvidia drivers? does it do that on all games? i play rimworld and they just released a recent update maybe that conflicted with your setup? reinstall rimworld after backup saves
I'm confused are you saying you download 400 to 500 on speed test but 50 on steam or the other way around?
400 Mbps = 50MB so if you're getting 50MB downloading on steam that's the same thing
i had a similar issue once turned out to be my heatsink was not on properly. another time had that issue my heatsink had clogged and water was not flowing fast enough through heat sink. another time my cpu was overclocked too much .