Place ¾ cup granulated sugar, brown sugar, and ½ cup butter in a large bowl; beat with a mixer at medium speed 3 minutes or until well blended. Add eggs, 1 at a time, beating well after each addition. Beat in pumpkin and vanilla. Lightly spoon 3 cups flour into dry measuring cups, and level with a knife. Combine flour and next 4 ingredients (through salt) in a bowl, stirring well with a whisk. Add flour mixture and ¾ cup buttermilk alternately to sugar mixture, beginning and ending with flour mixture.