Character controller updates less in fullscreen

I've made a simple hallway runner movement with walljumps, and when testing it in the small preview window, everything ran smoothly with no problems. However, whenever I try testing it at a higher resolution ("maximize on play" option or exported fullscreen), the character controller's movement updates less frequently. At first, I thought it was a huge framerate drop, until I put an animated part of the level onscreen and saw that it was moving at the desired framerate.

To move my character, I simply use a Vector3 called moveDirection, and use "controller.Move(moveDirection * Time.deltaTime);". Does anyone know what I'm doing wrong?

Code: float leftvelright = 0.0f; public float jumpSpeed = 10.0F; public float gravity = 30.0F; private Vector3 moveDirection = Vector3.zero; public static float runSpeed=5.0f; public static bool dead = false;

         void Update () {
             
             if (runSpeed < 20.0f) {
                 runSpeed = runSpeed + 0.05f*Time.deltaTime;
                 print (runSpeed);
             }
             
             if (dead == true) {
                 leftvelright = 0;
             }
     
             //print (leftvelright)
             
             CharacterController controller = GetComponent<CharacterController>();
     
             if (leftvelright < 5 && leftvelright >= 0 && Input.GetAxis ("Horizontal") > 0 || leftvelright > -5 && leftvelright <= 0 && Input.GetAxis ("Horizontal") < 0) {
                 leftvelright = leftvelright + (Input.GetAxis ("Horizontal") * Time.deltaTime * 50);
                 //steer
             }
             if (leftvelright <= 5 && leftvelright < 0 && Input.GetAxis ("Horizontal") > 0 || leftvelright >= -5 && leftvelright > 0 && Input.GetAxis ("Horizontal") < 0) {
                 leftvelright = leftvelright + (Input.GetAxis ("Horizontal") * Time.deltaTime * 50);
                 //reversedirection
             }
             if (Input.GetAxis ("Horizontal") == 0 && leftvelright < 0) {
                 leftvelright = leftvelright + (0-leftvelright)*10*Time.deltaTime;
                 //stop
             }
             if (Input.GetAxis ("Horizontal") == 0 && leftvelright > 0) {
                 leftvelright = leftvelright - leftvelright*10*Time.deltaTime;
                 //stop
             }
     
     
     
             if (leftvelright > 10)
                 leftvelright = 10;
             if (leftvelright < -10)
                 leftvelright = -10;
     
             if (controller.isGrounded) {
                 moveDirection = new Vector3 (leftvelright, 0, 0);
                 
                 if (Input.GetButton("Jump"))
                     moveDirection.y = jumpSpeed;
                 
             }
             moveDirection.x = leftvelright;
     
             moveDirection.y -= gravity * Time.deltaTime;
     
             moveDirection.z = runSpeed;
     
             controller.Move(moveDirection * Time.deltaTime);
         }
     
         void OnControllerColliderHit(ControllerColliderHit hit){
             if (hit.gameObject.tag == "Wall") {
     
                 moveDirection = new Vector3 (leftvelright, -1, 0);
     
                 if (Input.GetButton ("Jump")) {
                     moveDirection.y = jumpSpeed;
                     if (moveDirection.y > jumpSpeed)
                         moveDirection.y = jumpSpeed;
                     leftvelright = -leftvelright * 2.0f;
                 }
             }
         }