Moving up and down (in a slope) without change to velocity or "bumping"

Maybe I'm using the wrong terminology, but here goes anyway.

I have a player object. It's a capsule with a Rigidbody (use gravity on, Freeze Rotation Constraints on X and Z), a Box collider (size 1, 2, 1) and a player script created by me (below).

Every time I get the player to go over a "pad" (also below), it "stops" a little bit on the edge, losing some speed in the process. The pad has two mesh colliders attached to it (one for the "outer" part, another for the "inner" part).

I'm wondering how I could achieve a behaviour that allows my player to board the pad without losing any speed (to the physics geeks - like myself: I know that, since there is a slight slope, the velocity in the plane will change a little bit. That's not my point. I'm talking about the modulus of the velocity vector).

Here's the pad I made (feel free to grab it and use yourself):

Full assets: https://www.dropbox.com/sh/wgyx356lh9e53fr/_aI5Amsb1F

Here's the movement part of the player script:

 function Update () {
     var x : float;
     var z : float;
     
     if (Input.GetButton("Horizontal")) {
         x = Input.GetAxis("Horizontal");
         moveX = true;
     }
     else {
         x = 0;
         moveX = false;
     }
     
     if (Input.GetButton("Vertical")) {
         z = Input.GetAxis("Vertical");
         moveY = true;
     }
     else {
         z = 0;
         moveY = false;
     }
     
     if (moveX || moveY) {
         if (x > 0) _x = 1;
         else if (x < 0) _x  = -1;
         else _x = 0;
     
         if (z > 0) _y = 1;
         else if (z < 0) _y  = -1;
         else _y = 0;    
  
         var movement = Vector3( _x, 0, _y );
     
         movement *= Time.deltaTime * speed;
     
         if (movement != Vector3.zero) {
             transform.position += movement;
             transform.rotation = Quaternion.LookRotation(movement);
         }
     }
     UpdateCamera();
 }

Edit: Changed the title for better description of the problem