Preheat oven to 350 F degrees. Grease & flour loaf pan. In large bowl, sift together the flour, sugar, baking soda, baking powder and salt TWICE. In a medium bowl, combine the pumpkin, eggs, oil, vanilla and sour cream until smooth. Make a well in the flour mixture and pour in the wet ingredients. Whisk together until smooth. Fold in 1 cup of chocolate chips. Pour into prepared loaf pan. Sprinkle 1/4 cup chocolate chips on top. Bake 55-60 minutes or until a toothpick comes out clean. Cool in pan on a wire rack 20 minutes before removing to wire rack to cool completely.