PREHEAT oven to 350Â°F. Grease 13x9-inch baking pan; set aside. Beat cake mix, pumpkin, dressing and eggs in large bowl with electric mixer on medium speed until well blended. Pour into prepared pan.
BAKE 32 to 35 min. or until wooden toothpick inserted in center comes out clean. Cool completely in pan on wire rack.
BEAT cream cheese, butter, milk and vanilla in large bowl with electric mixer on medium speed until well blended. Gradually add sugar, beating after each addition until well blended. Spread over cooled cake. Cut into pieces to serve. Store any leftovers in refrigerator.