DUDE, I had the same issue, I switched from a i7-4790k to the 16 Core Threadripper!
The PC was so slow in opening apps (chrome took 5-10 seconds to start)
I MANAGED TO FIX THE ISSUE BY INSTALLING THE SAMSUNG MAGICIAN SOFTWARE AND TURNING ON THE S.M.A.R.T TECHNOLOGY FOR MY SAMSUNG 860 SSD 1TB.
FUNNY THING: I contacted AMAZON.CA and told them that the performance of the threadripper was not as I expected (after 2 months of having the CPU)
the AMAZON rep was soo00o nice and gave me a full refund for both my CPU and Motherboard (~$1700) and told me that I DON'T EVEN HAVE TO SEND THE CPU AND MOTHERBOARD BACK!