All code is from examples.
Yes, problem is still here. Ok, some order in all that chaos I've wrote:) Here's where I'm at now. A bit modded setup: stepper with gearbox, same driver, Arduino Uno. Driver set to 2 microstep (lowest possible).
Accelstepper library example (const. speed, proportional control) works ok (with some jitter thou). The most reliable movement was achieved with speed of 200. But, if while movement, motor behaves normally, when it stops, it starts to jitter. Also, speed of 200 is to low for me, because gearbox (worm gearbox) is 1:100.
Trying example from library written by Laurentiu Badea, BasicStepperDriver, motor spins fast with no jitter even with gearbox.
Again, the reason I want to use Accelstepper is that I need to control 2 steppers simultaneously by 2 pots.