In a bowl, dissolve yeast in warm water. Sprinkle with sugar; let stand for 5 minutes. Add milk, brown sugar, pumpkin, butter, salt, spices and 2 cups flour; beat until smooth. Stir in enough remaining flour to form a soft dough. Turn onto a floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour. Punch dough down.