Can you paste your actual code so we can see how you are calling it?

Are you using Random.seed to seed your Random number generator?

I made this test script:

public class TestCode : MonoBehaviour {

float fHighestNumber = 0;
float n = 150;

void 
Start () 
{
    for(int i = 0; i < 10000; i++)
    {
       float fRandomNumber = Random.Range(0, n);

       if(fHighestNumber < fRandomNumber)
         fHighestNumber = fRandomNumber;
    }
    Debug.Log (fHighestNumber);
}

}

And the results proved my question false. After that, it seems the problem is here:

[HideInInspector] public Vector3 vMAP_SIZE = new Vector3 (20000, 0, 20000);

Somewhere in my code it sets the vector (50, 0, 50). Just cant seem to find where. That number gets multipled by 3, therefore we get 150.