Well you should have high rapid speeds due to high pitch but this obviously depends on pulley sizes thou with 3:1 ratio I can guess at around 25-35mm pitch.
With only 36V then you'll have lower speed and there fore torque from the motors than they are capable of so for this reason I suggest you keep the motor tuning down so the motors are in the lower Rpm range where more torque is available.

Like I mentioned before your problem could come from lack of resolution and motors running too slow causing rough movement.?