Thanks for the links.
Well, as noted before, this is example that came with library. There wasn't any accel setup. Anyway, I've tried it with no luck. Also, I've tried other microstepping setting on driver, but without significant improvement.
Motor does rotate good, but when it stops in certain position, it starts hard jittering.
I do not need acceleration, I just need to control two steppers proportionally with given signal. In real setup I plan to use rc tx/rx. So I map pwm signal to needed amount and use that amount for stepper control. So the main problem it jitter. I've tried filtering suggested in another threads, but it doesnt help nearly at all.
Also, testing Constant speed example from Accelstepper library, the movement is sort of clacky. Don't know how to describe it correctly. While trying Laurentiu Badea BasicStepperDriver example, rotation is clean and constant. And sounds much better.
Motor model is 86HS15560A4, nema34 btw, it's a huge motor. I've tried this setup with much smaller nema17, but with similar results.