Melt 1-1/2 cups peanut butter chips. Beat cream cheese, powdered sugar and 1/3 cup milk in medium bowl until smooth. Add melted chips; beat well. Beat in remaining 2 tablespoons milk. Spread into cooled crust.
Sprinkle gelatin over cold water in small bowl; let stand 1 minute to soften. Add boiling water; stir until gelatin is completely dissolved. Cool slightly. Combine sugar and cocoa in medium bowl; add whipping cream and vanilla. Beat at medium speed until stiff; pour in gelatin mixture, beating until well blended. Spoon into crust over peanut butter layer. Refrigerate several hours. Garnish with remaining chips. Cover; store leftover pie in refrigerator.