Prepare pudding as per package directions, with the 3c. milk. Fold in Cool Whip. Cover the bottom of a 13x9" pan with graham crackers. Cover with half the pudding mixture, another layer of graham crackers, the remainder of the pudding and top with a layer of graham crackers.
Combine margarine, chocolate, syrup, vanila, sugar, and 3T milk. Pour glaze over cake; refrigerate until ready to serve.