Follow an object (mouse click) without decreasing the speed

hello,

i want to make a movie clip follow the mouse while we are pressing the left Button (NOT "be" the mouse ), i end it up with this code but am having a problem,

-the speed of the movie clip decrase by his own, i know that this is happening because of the last two lines, i will be glad if anyone could help me to solve this problem, thanx

onClipEvent (enterFrame) {

          onMouseUp = function ()

          {

                    apui = false;

          };

          onMouseDown = function ()

          {

                    apui = true;

                    rotateSpeed = 3;

          };

          if (apui == true)

          {

                    goX = _root._xmouse;

                    goY = _root._ymouse;

}

          else if (apui == false)

          {

                    goX = this._x;

                    goY = this._y;

          }

          this._x -= (this._x - this.goX)/20 ;

          this._y -= (this._y - this.goY)/20 ;

}