Preheat oven to 325°F (170°C). Spray an 8½x4½-inch loaf pan with baking spray with flour. Line pan with parchment paper, letting excess extend over all sides of pan.

In a large bowl, whisk together flour, pie spice, baking powder, salt, and pepper.

In a medium bowl, whisk together pumpkin, granulated sugar, oil, brown sugar, eggs, and vanilla until smooth. Fold pumpkin mixture into flour mixture until smooth. Spread batter into prepared pan. Firmly tap pan on a kitchen towel-lined counter to settle batter. Using an offset spatula dipped in oil, score a line down center of batter, leaving about a 1-inch border on short sides of pan.

Bake until a wooden pick inserted in center comes out with a few moist crumbs, 1½ hours to 1 hour and 40 minutes. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack. Store in an airtight container for up to 3 days.