Why is my large NEMA 34 stepper motor so weak?

Question

I bought this motor from StepperOnline. It's a NEMA 34 stepper motor 6.0 A 4.5 Nm.

I wired it like this (not to scale):

But I am using a variable power supply.

I have the power supply set to 30 V and 6 A, but the motor can only lift about 5 pounds. I noticed that it never uses more than 1.2 A. I tried playing around with different speeds and switch settings.

Here is current switch configuration:

Why can this large stepper motor only lift 5 pounds? I was expecting it to lift way more. Also, why is it only using a max of 1.2 A instead of the rated 6 A?

Edit:

Here is my setup. I had some rope at the end of the 3D printed part, which was holding some weight. The rope was 9cm away from the motor shaft.

Edit 2:

Here is the board:

Here is the Arduino code:

#define driverPUL1 2  // PUL pin 1
#define driverDIR1 3  // Dir pin 1
#define enablePIN1 4  // enable pin 1

#define potPin A0

void setup() {
  pinMode(driverPUL1, OUTPUT);
  pinMode(driverDIR1, OUTPUT);
  pinMode(enablePIN1, OUTPUT);

  Serial.begin(9600);
  Serial.println("setup");
}

void loop() {
  digitalWrite (driverDIR1, HIGH);
  digitalWrite (enablePIN1, HIGH);

  int value = map(analogRead(potPin), 0, 1023, 255, 0);
  Serial.println(value);

  if (value !=  255) {
    digitalWrite(driverPUL1, HIGH);
    delayMicroseconds(value);
    digitalWrite(driverPUL1, LOW);
    delayMicroseconds(value);
  }
}

Here's a picture of the power supply while I'm holding the motor still with my hand (applying only about 5 pounds), you can see that it's only using 1 A.

My power supply is set to 6.4 A:

Answer 1

Set 2 or 4 microsteps (it's 400 or 800 on driver); setting 6400 is the reason why you have little torque (only 4,9% of maximum torque). Higher voltage is essential too, but your voltage should be OK for holding still objects or slow motion.

(Image source: Faulhaber - Stepper Motor Tutorial - Microstepping Myths and Realities)