In a medium saucepan, mix the milk and pudding mix with wire whisk. Cook over medium heat until the mixture comes to full rolling boil, stirring frequently. Remove from the heat and place a sheet of plastic wrap directly on the surface of the pudding. Cool to room temperature, about 45 minutes. Fold in 1/2 cup of the sour cream. Place 1 layer of banana slices in the bottom of the crust. Spread half of the pudding over the bananas. Repeat the layers, covering banana slices completely. Cover and refrigerate for 3 hours before cutting. Just before serving, mix the remaining 1/2 cup of sour cream and sugar. Spread over the top of the pie.