You’re certainly not the only one. This thread is shaping up nearly identically to every post I’ve seen on the stuttering issue. I myself have been seeking an answer to this problem for a very long time with no success. We’re just seeing fewer posts about it these days. Here’s a link posted a while back that may help you somehow.
When the mounts update was released, it almost eliminated the stuttering for me, but it came back upon release of the 12/19 hotfix. I don’t believe your PC has anything to do with it especially in light of the fact that you’ve run the game in the past with no issue. For me, the only thing that’s ever made any difference either way has been an update, patch, or hotfix. This issue is probably a result of game design.
I’m done looking for answers and currently can’t even play the game. Good luck in taking up the mantle should you choose to do so.