Mix pudding with milk and add cool whip. Line bottom of 9" x 13" pan with graham crackers. Top with half the pudding mixture. Make a second layer with graham crackers and pudding. Top with crackers. Refrigerate.
For the topping: Melt margarine in a large saucepan. Add corn syrup, milk, cocoa, and oil. Mix and bring to a boil. Remove from heat and add vanilla. Add usgr and mix in a blender on medium speed until smooth. Pour over cake and refrigerate. Enjoy!!