Pour 2 cups milk, pudding mix, peanut butter and banana into container with tight-fitting lid and shake until well blended, or put into blender container and blend on medium speed 1 minute or until smooth. Pour into large pitcher. Add remaining 1 ½ cups milk; stir until blended.
Serve at once or refrigerate and stir before serving. Mixture thickens as it stands. Thin with additional milk, if desired.