Preheat oven to 350°. Line bottoms of 3 greased 9-in. round baking pans with parchment; grease paper., In a large bowl, combine cake and pudding mixes. Add eggs, 1 at a time, beating well after each addition. Gradually beat in Dr Pepper and vanilla., Transfer batter to prepared pans. Bake until top springs back when lightly touched, 20-25 minutes. Cool in pans 10 minutes before removing to wire racks; remove paper. Cool completely., For frosting, in a large bowl, beat cream cheese and butter until smooth. Beat in cocoa. Add confectioners' sugar and vanilla; beat until creamy., Place 1 cake layer on a serving plate; spread with 1/2 cup frosting. Repeat layers. Top with remaining cake layer. Frost top and sides of cake with remaining frosting.