In a large bowl, mix flour, baking soda, baking powder, cinnamon, nutmeg, ginger, allspice, and salt together.
In a separate bowl, whisk pumpkin and brown sugar together until combined. Add in oil, eggs, vanilla extract, and sour cream. Mix until well combined.
Add the dry ingredients to the wet ingredients, and stir until all ingredients are well incorporated.
Pour the batter into the pan. Spread the crumb topping evenly over the batter. Lastly, sprinkle the remaining chopped pecans evenly over the crumb topping.
Bake for 28-30 minutes, or until a cake tester comes out clean. (If the top looks like it's getting too brown, cover it with foil, and let it finish baking.)
Serve warm, at room temperature, or cold.
Enjoy!