The stutter happens when you're in Kingdom, it's especially apparent when you're riding a horse. Nothing can fix it.
I recall reading it was an issue with Nvidia cards.
But I found a way to not notice stutters anymore. You must dim the screen, everything including gamma and brightness should be as low as possible.
The way I discovered this is that on my Laptop where the screen was far less bright than my Desktop screen; I would never notice any stutters/hitches on the laptop whereas they'd drive me crazy on the Desktop. So I dimmed the Desktop screen and voila, I rarely get bothered by stutters anymore.