Line pan with whole graham crackers. Mix pudding, using only 3 1/2 cups of milk. Fold in whipped topping. Pour 1/2 of the pudding over graham crackers. Add 2nd layer of crackers and rest of pudding. Add a 3rd layer of crackers.
Top with special frosting: Combine chocolate, karo syrup, vanilla, margarine, powdered sugar and milk with a hand mixer. Spread over the top of graham crackers and refrigerate overnight.