PROBLEM SOLVED:
It was a program conflict - I had a friend suggest going through the processes and ‘End Task’ on each one until the performance for UE4 was normal. So I was doing this through tons of them with no success. But then I did it on Realtek Audio Manager - and boom… CPU performance went from 100% down to like 30-50 and UE4 was full operational!
Interestingly, I wanted to confirm this, so I restarted my PC so I could do it all over again. And UE4 worked fine. So maybe by killing the process, I cleared a cache that was causing the issue?
Can’t be 100% sure, but just know - if UE4 is so slow its unusable (in both UI/Viewport) then try killing processes as it might be a program conflict.
Thanks for everyones help!
Darren