Sprinkle yeast over warm water in large bowl. Add 1 teaspoon of the granulated sugar; let stand until foamy, about 5 minutes. Beat in remaining 2 tablespoons sugar, the eggs, butter and pumpkin.
Gradually add 5 cups of the flour and the salt, scraping side of bowl, until soft dough forms. Turn out onto floured surface and knead remaining 1/2 cup flour into dough, adding more if sticky. Knead for 10 minutes, until smooth. Dough will be soft.
Grease a bowl; add dough. Cover with plastic wrap and place in a warm spot until doubled, about 1-1/4 hours.
Coat two 13x9x2-inch baking pans with nonstick cooking spray. Make Filling: Mix butter, granulated and brown sugars, and cinnamon in a bowl.
Punch down dough. Roll out half onto a lightly floured surface to form a 16 x 10-inch rectangle. Spread with half of the filling. Starting on one long side, roll up jelly-roll fashion. Pinch seam to close. Repeat with second half of dough and filling.
Cut each log crosswise into 12 generous 1-inch pieces. Arrange 12 pieces, cut-side down, in each prepared pan. Cover with plastic wrap; let sit in a warm spot until buns double in size, about 30 to 45 minutes. (You can refrigerate one pan overnight or cover plastic with foil and freeze at this point. Thaw in fridge overnight, then thaw on counter while preheating oven.)
Heat oven to 350°. Uncover pans and bake buns until they are golden brown and bubbly, 28 to 33 minutes (thawed buns, 36 minutes). Transfer to a wire rack; let cool 10 minutes.
Blend confectioners' sugar and milk. Drizzle over buns (about 1/3 cup per pan). Serve warm.