In a mixing bowl, beat pumpkin, 2 cups white sugar, and oil. Add eggs, and mix well.
In another bowl, combine flour, baking soda, cinnamon and salt. Add these dry ingredients to the pumpkin mixture, and beat until well blended. Pour batter into a greased 15 x 10 inch baking pan.
Bake at 350 degrees F (175 degrees C) for 25 to 30 minutes, or until cake tests done. Cool.
In a mixing bowl, beat the cream cheese, butter or margarine, and vanilla until smooth. Gradually add 1 3/4 cups confectioners' sugar, and mix well. Add milk until frosting reaches desired spreading consistency. Frost cake, and sprinkle with nuts.