Preheat oven to 350°F. Grease and line a 9x5-inch loaf pan.
Whisk flour, baking soda, baking powder, salt, and spices in a large bowl.
In another bowl, whisk pumpkin, sugars, eggs, oil, and vanilla until smooth.
Add dry ingredients to wet. Stir gently until just combined.
Stir in milk to loosen the batter. Fold in nuts or chips, if using.
Scrape batter into the pan and smooth the top.
Bake 55 to 65 minutes, until a tester has a few moist crumbs.
Cool 15 minutes in the pan. Transfer to a rack to cool completely.