Preheat oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a medium bowl, whisk together flour, baking soda, baking powder, salt, and pumpkin pie spice.
In a large bowl, beat pumpkin puree, granulated sugar, brown sugar, oil, eggs, and 1 teaspoon vanilla until smooth.
Gradually fold the dry ingredients into the wet ingredients until just combined.
Transfer batter to the prepared loaf pan and bake for 60 minutes, or until a skewer inserted in the center comes out clean.
Cool the bread completely on a wire rack before frosting.
To make the frosting, beat cream cheese and butter until smooth, then add powdered sugar and 1/2 teaspoon vanilla, mixing until creamy.
Spread the frosting over the top of the cooled loaf and slice.