Anyway, I found the solution myself, in case someone else has problems.
The solution is to set refresh rate to 60Hz and turn VSYNC On, because the mouth animations are not properly timed, but tied to number of frames. It probably affects only people with 120Hz monitors.
I hate to grave dig your post, but I can't seem to make a new post on here. My monitor is at 60Hz by default, yet I experience the mouth moving too fast problem. My monitor can do 4K, but it is set to 1080p right now so I don't think that is the problem. Any suggestions?