Reading what you have said, that you had the stuttering issue prior to the virus and after the in-place Windows 10 upgrade, I would suggest that it appears to be software-related.
A few people seem to point to either the Dell support apps and/or Windows Sonic for headphones.
You said that the USB NIC caused DPC (Deferred Procedure call) issues, did you run DPC latency monitor and see what it reported?
Hope this helps.
