Preheat oven to 350 degrees. Prepare cake batter according to box directions. Pour 1/2 of batter into a 9 x 13" pan. Bake at 350 degrees for 15 minutes. Melt caramels, margarine, and evaporated milk. Blend well, and pour mixture over the hot cake. Sprinkle chocolate chips and pecans over caramel mix. Top with rest of cake batter, and bake for an additional 15 minutes in a 350 degree oven. Frost with favorite chocolate frosting, if desired. ----