Heat the oven to 350 degrees. Spray 2 (8 1/2x4 1/2 or 9x5-inch) loaf pans with cooking spray.
In a large bowl, beat the butter and sugar with an electric mixer on medium speed until mixed. Add the eggs 1 at a time, beating well after each addition. Add the pumpkin, sour cream and vanilla. Beat on low speed until mixed. Beat on medium speed until the batter is smooth and creamy, scraping the sides of the bowl.
Add all of the remaining ingredients. Beat on low speed until moistened. Beat on medium speed until the batter is thick and creamy.
Spread evenly in the pans. Bake for 55 to 60 minutes or until a toothpick inserted in the center comes out clean.
Let the loaves cool in the pans for 10 minutes. Run a knife around the edges of the pans to loosen the bread. Remove from the pans to a cooling rack. Cool completely (about 1 hour). Wrap securely to store. To freeze one loaf, over-wrap it or place it in a freezer bag.