How to set up PID values and Effort Limits for Linear actuator controller mounted on an AGV

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Background

I have a lead-screw linear actuator mounted vertically on an AGV. It is powered by a Nema 17 stepper motor and moves at a constant speed of 1.5 m/minute (0.025 m/s) when stepper motor speed is set to 600 steps/minute.

Problem

I was trying to model the linear actuator in URDF for simulation testing in gazebo. However I was struggling to figure out how to simulate the specs above. By tinkering with the PID values, I managed to get roughly the correct speed when the actuator is moving up, however, when moving down, the actuator just seems to fall rapidly in simulation.

The PID values I used were:

P: 7000 I: 1.0 D: 10.0

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