Creating characters that can move on their own. Problems adding Z Axis to movement.

Everything works great on the X and Y but im getting no movement on the Z axis. Im sure im overlooking something I just cant spot it. Help!

public class MoveBox : MonoBehaviour { //Variables int speed; //creates a speed variable Vector3 dir; //this control the direction string myDir; // this will float maxX, maxY, minX, minY, minZ, maxZ; //boundaries for the cube

 // Use this for initialization
 void Start () {
     //choose a random speed.
     speed = Random.Range(8,16);
     ChooseBarrier ();
     ChooseDir();
 }
 void ChooseBarrier(){
     //sets the Max and Min Values
     maxX = Random.Range(6,16); // sets Max X to between 10 and 16
     minX = -maxX; // this sets the min X value to be the negative of the Max X value
     maxY = maxX; // this sets the Max Y value to be the same as the Max X
     minY = minX;// this sets the  Min Y to be the same as the Min X
     minZ = minX;
     maxZ = maxX;    
     

 }
 void ChooseDir(){   // choose the direction -- call a choose diretion function
     ChooseBarrier ();
     // create a temporary int to determine direction
     int whichWay = Random.Range (0, 4); // 0 will be right, 1 will be down, 2 will be left, 3 will be up, 4 will be forward, 5 will be backward
     switch (whichWay) {
     case 0: // if which way equals 0
         dir = Vector3.right;
         myDir = "right";
         break; //ends the action
     case 1: //if which way equals 1
         dir = Vector3.down;
         myDir = "down";
         break; //ends the action
     case 2: //if which way equals 2
         dir = Vector3.left;
         myDir = "left";
         break; //ends the action
     case 3: //if which way equals 3
         dir = Vector3.up;
         myDir = "up";
         break; //ends the action
     case 4:
         dir = Vector3.forward;
         myDir = "forward";
         break; //ends the action
     case 5:
         dir = Vector3.back;
         myDir = "backward";
         break; //ends the action
     }
 }
 void Move(Vector3 direction){
     transform.Translate (direction * speed * Time.deltaTime); // this will make the character move at a speed and direction
 }

 void checkPos (string direction){ // this will check the direction and determine if there is a barrier
     switch (direction) {

     case "right": // if {direction == Vector3.down}
         if (transform.position.x > maxX) {
             ChooseDir ();
         }
         break;
     case "down":
         if (transform.position.y < minY) {
             ChooseDir ();
         }
         break;
     case "left":
         if (transform.position.x < minX) {
             ChooseDir ();
         }
         break;
     case "up":
         if (transform.position.y > maxY) {
             ChooseDir ();
         }
         break;
     case "forward":
         if (transform.position.z > maxZ) {
             ChooseDir ();
         }
         break;
     case "backward":
         if (transform.position.z < minZ) {
             ChooseDir ();
         }
         break;
     }
 }
 // Update is called once per frame
 void Update () {
     Move (dir); // calls the move function using the dir variable to determine direction
     checkPos(myDir); // check
 }

}