Prepare yellow cake mix as directed. Cook and cool cake. Mix milk, sour cream, and vanilla instant pudding. Spread over cooled cake. When using strawberries, slice them 1/4-inch thick and lay over all the pudding mixture. When using raspberries, put a solid layer of berries over the pudding mixture. Cover fresh fruit with lite Cool Whip (softened). Make a day ahead, refrigerate. Can garnish with fresh berries if you want.