Memory Leak? Game slowing down

I'm currently experiencing a problem which I'm sure is a result of my poor understanding of programming concepts. My problem is this: every time I call the function to rebuild my level, the game progressively slows down. I've tried to clear everything, but somehow something is still causing the slow down. I'll attach a zip with all of the files, and also I will add the main code to this. Any help us much appreciated!

The attempted clearing happens in a function called cleanup() and the level setting up in setupLevel().

PHP Code:

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//KESLER
package {
    import flash.display.Sprite;
    import flash.geom.Rectangle;
    import flash.geom.Point;
    import flash.display.Bitmap;
    import flash.display.BitmapData;
    import flash.events.KeyboardEvent;
    import flash.events.Event;
    import flash.ui.Keyboard;
    import Queue;
    import flash.text.StaticText;
    import flash.system.*;

    //class declaration
    public class tileEngine extends Object {
        //declare variables
        //declare variables
        private var mapW:int;
        private var mapH:int;
        private var screenY:int;
        private var screenX:int;
        private var tileX:int;
        private var tileY:int;
        private var tiles:Sprite;
        private var level:int;
        private var levelLength:int;
        private var border:Sprite;
        private var r:Sprite;
        private var screen:Sprite;
        private var cover:Cover;
        private var updateTimer:Number;
        private var scrollSpeed:Number;
        private var gamePaused:Boolean;
        private var queue:Queue;
        private var keysPressed = [false, false, false, false];
        private var keyCounters = [0,0,0,0];
        private var guy1up:int = 65;
        private var guy1down:int = 90;
        private var wall:int = 8;
        private var levelPassedDelay:int;
        public var guy1:Character;
        public var lastKeyChange:String;
        public var gui:GUI;
        private var map:Array;
        private var stats:Stats;
        //class constructor function
        public function tileEngine (rootMC:Sprite) {
            r = rootMC;
            screenY = 450;
            screenX = 450;
            tileX = 40;
            tileY = 40;
            level = 1;
            setupLevel();
        }
        private function setupLevel():void {
            r.addEventListener(Event.ENTER_FRAME,updateGame);
            gamePaused = false;
            scrollSpeed = 3;
            levelPassedDelay = 0;
            updateTimer = tileX;
            buildMap();
            buildBorder();
            buildGUI();
            buildCharacters();
            stats= new Stats();
            r.addChild(stats);
        }
        public function buildMap():void {
            tiles = new Sprite();
            r.addChild(tiles);
            tiles.y = 5;
            map = Maps.getMap(level);
            levelLength = (map[0].length*tileX-300); //length of level in pixels
            var x1:int = Math.ceil(screenX/tileX)+1; //give the screen a little buffer
            var y1:int = Math.floor(screenY/tileY);
            queue = new Queue();
            for(var n=0; n<x1;n++) {
                var column:Sprite = new Sprite();
                column.x=n*tileX;
                for(var m=0;m<y1;m++) {
                    var tile:Tile = new Tile();
                    tile.type = map[m][n];
                    tile.gotoAndStop(tile.type);
                    tile.x = 0;
                    tile.y = tileY*m;            
                    column.addChild(tile);
                }
                tiles.addChild(column);
                queue.push(column);
            }
        }
        private function buildBorder():void {
            border = new Sprite();
            border.graphics.lineStyle(10, 0x00000);
            border.graphics.drawRect(4, 4, 442, 442);
            border.graphics.endFill();
            r.addChild(border);
        }
        private function buildGUI():void {
            gui = new GUI();
            gui.key1.gotoAndStop(3);
            gui.key2.gotoAndStop(4);
            r.addChild(gui);
        }
        private function buildCharacters(){
            guy1up = 65;
            guy1down = 90;
            guy1 = new Character();
            guy1.isDead = false;
            guy1.ID = "guy1";
            guy1.claimedPos = Maps.getCharPos(level)[0];
            guy1.x = 70;
            guy1.y = guy1.claimedPos*tileY+guy1.radius;
            guy1.keyUP = 1;
            guy1.keyDOWN = 2;
            r.addChild(guy1);
        }
        private function updateGame(event:Event):void {
            if(!gamePaused) {
                scrollScreen();
                moveCharacters();
            } else {
                levelPassed();
            }
        }
        private function levelPassed() {
            if(levelPassedDelay==0) {
                cover = new Cover();
                r.addChild(cover);
            } 
            if(levelPassedDelay < 120) {
                guy1.x+=guy1.speed;
                levelPassedDelay++;
            } else {
                level++;
                cleanup();
                setupLevel();
            }
        }
        private function cleanup() {            
            r.removeChild(cover);
            r.removeChild(tiles);
            r.removeChild(guy1);
            r.removeChild(gui);
            r.removeChild(border);
            r.removeChild(stats);
            queue = null;
            r.removeEventListener(Event.ENTER_FRAME,updateGame);
            flash.system.System.gc();
            flash.system.System.gc();
        }
        private function scrollScreen():void {
            if((screenX-tiles.x+tileX) > levelLength) {
                gamePaused = true;
            } else {
                tiles.x-=scrollSpeed;
                updateTimer-=scrollSpeed; //this timer controls when new tiles are created and removed
                if(updateTimer < 1) {
                    updateMap();
                }
            }
        }
        private function updateMap() {
            updateTimer+=tileX;
            tiles.removeChild(queue.pop());
            var curColumn:int = Math.ceil((screenX-tiles.x)/tileX)+1; //calculates the column of tiles to add
            var y:int = Math.floor(screenY/tileY); //how many rows
            var column:Sprite = new Sprite();
            column.x = (curColumn-1)*tileX;
            for(var i=0;i<y;i++) {
                var tile:Tile = new Tile();
                tile.type = map[i][curColumn];
                tile.gotoAndStop(tile.type);
                tile.y = tileY*i;            
                column.addChild(tile);
            }
            queue.push(column);
            tiles.addChild(column);
        }
        private function moveCharacters(){
            if(guy1.isDead) {
                hitWall();
            }
            if(!guy1.isDead) {
                var updatedPos = Math.floor((guy1.claimedPos*tileY-guy1.y+guy1.radius)/guy1.speed);
                if(updatedPos < 0) {
                    guy1.y-=guy1.speed;
                } else if(updatedPos > 0) {
                    guy1.y+=guy1.speed;
                }
            } else
                guy1.x-=scrollSpeed;
            checkCurrentTile(guy1);
        }
        
        public function checkCurrentTile(guy:Character):void{
            var xTile = Math.floor((-1*(tiles.x-guy.x+(guy.radius*2)))/tileX)+2;
            var yTile = Math.floor(guy.y/tileY);
            var tile_type = map[yTile][xTile];
            if(tile_type > wall) {//WALL
                guy.isDead = true;
            }
        }
        private function hitWall():void {
            if(levelPassedDelay==0) {
                updateTimer+=1000;
                scrollSpeed=.2;
                cover = new Cover();
                r.addChild(cover);
            } 
            if(levelPassedDelay < 120) {
                levelPassedDelay++;
            } else {
                cleanup();
                setupLevel();
            }
        }
        private function checkWall(guy:Character,dir:String) {
            if(dir == "up") {
                var addition = -1;
            } else {
                var addition = 1;
            }
            var xTile = Math.floor((-1*(tiles.x-guy.x+(guy.radius*2)))/tileX)+2;
            var yTile = guy.claimedPos+addition;
            var leftTile = map[yTile][xTile-1];
            var middleTile = map[yTile][xTile];
            var rightTile = map[yTile][xTile+1];
            if(leftTile > wall && middleTile > wall && rightTile > wall)
                return false;
            return true;
        }
        public function keysDown(event: KeyboardEvent): void{
            if(event.keyCode == guy1up){
                if(guy1.claimedPos > 1)
                    if(checkWall(guy1,"up"))
                        guy1.claimedPos--;
            }
            if(event.keyCode == guy1down){
                if(guy1.claimedPos < 10)
                    if(checkWall(guy1,"down"))
                        guy1.claimedPos++;
            }
        }
    }
} 


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In case anyone was interested, I figured out an alternative solution. I never could find out what was causing my game to slow down, although I believe it was tied to the tiles and the uncertainty of garbage collection.

In the end I changed my code to recycle objects and reuse them rather than remove them and create new ones. Works like a charm this way.