Prepare cake mix according to package directions for a 9x13 cake. Once cake comes out of oven, allow to cool for just a couple of minutes.
Then with a wooden spoon handle or some other similar sized object, begin poking holes in the cake. You want the holes big enough so the pudding has plenty of room to get down in there. Be sure you poke right down to the bottom of the cake.
In a bowl, whisk together instant pudding with 4 cups of milk. Stir until all the lumps are gone. Pour pudding over cake . Taking care to pour it right in the holes as much as possible.
Spread it all out and using the back of the spoon gently push down into the holes. Put cake into the refrigerator to set at least 2 hours. Once cake is cooled, spread on whipped topping.
Crush the cinnamon graham crackers in a ziplock bag and crush them with a rolling pin. Leave some big pieces to have a bit of a crunch .
Sprinkle crushed graham crackers onto the top of the cake. Keep refrigerated.