Sift together 2 cups all-purpose flour, 1 teaspoon baking powder, ¾ teaspoon baking soda, 2 ½ teaspoons pumpkin pie spice and ¼ teaspoon salt in a medium bowl. Reserve.
Beat ¾ cup white sugar, 6 tablespoons brown sugar and ⅔ cup vegetable oil until smooth and well combined in a large mixing bowl.
Add 3 large eggs, one at a time, beating well after each addition.
Add ¾ cup pumpkin puree, ¾ teaspoon vanilla extract and 3 tablespoons milk, and beat until fully incorporated.
Add the dry ingredients to the pumpkin mixture in 2 parts, beating on low speed *just* until integrated. Be careful not to overmix, as this can make the cakes tough.
Spoon the batter evenly into the prepared pans, filling each ¾ of their capacity.
Bake for about 20 minutes, or until a toothpick or cake tester inserted in the center of a cake comes out clean.
Allow the pan to cool on a wire rack for 15 minutes, then carefully remove them onto the wire rack to cool completely.