rigidbody.AddForce jump, different heights each time

Hello, I would think that my code would work fine for jumps, but each time I jump the height is different. It changes with x velocity for some reason, is there some way to make it consistent? could it have something to do with the Delta time?

relevant code:

 function Update () {
 
 animTimer++;
 
 rigidbody.AddForce(Input.GetAxis("Horizontal") * horizontalSpeed * Time.deltaTime * 60,0,0);
 rigidbody.velocity.x = Mathf.Clamp(rigidbody.velocity.x,-6,6);
 
 if (Input.GetKeyDown(KeyCode.UpArrow) && isGrounded)
     {
         rigidbody.AddForce(0,jumpSpeed * Time.deltaTime * 60,0);
     }
 
             if (animTimer >= animSpeed)
                 {
                     frame++;
                     animTimer = 0;
                 }
                 
 if (Input.GetAxis("Horizontal") < 0) //if I'm pressing right
     {
     lastKeyPressed = "left";
         if (isGrounded)
                 {
         animLayer = 0;
                 }
         else
                 {
         animLayer = 4;
                 }
         
     }
 if (Input.GetAxis("Horizontal") > 0) //if I'm pressing right
     {
     lastKeyPressed = "right";
         if (isGrounded)
             {
     animLayer = 1;
             }
         else
             {
     animLayer = 5;
             }
         
     }
 
 if (!Input.GetAxis("Horizontal") && isGrounded) //if I'm pressing right
     {
         if (lastKeyPressed == "right")
             {
                 animLayer = 2;
             }
         if (lastKeyPressed == "left")
             {
                 animLayer = 3;
             }
     animTimer = 0;
     frame = 0;
     }
 
     rigidbody.velocity.x = rigidbody.velocity.x * friction;
         
         renderer.material.mainTextureOffset = Vector2(xOffset * frame, yOffset *animLayer);
 }
 
 function OnCollisionStay()
     {
         isGrounded = true;
     }
     
 function OnCollisionExit()
     {
         isGrounded = false;
     }