Prepare the pudding separately as per the package directions, but using 1 1/2 cups milk for each. Refrigerate.
In a large bowl, beat the whip cream until thick. Fold the prepared vanilla pudding into the whipped cream.
Spread the pudding on the double crackers almost to the edges, then set aside. Spread the same number of crackers with chocolate pudding and with vanilla pudding.
Assemble the cake by standing the crackers up, alternating chocolate and vanilla covered crackers. The cake will be 2 crackers wide, and 1 cracker high. After sticking the pudding covered crackers together, frost the outside of the cake with the remaining vanilla pudding.
Refrigerate the cake several hours or overnight. Before serving, pour rows of chocolate syrup over the cake, letting it run down the sides.
Cut slices of the cake at a 45 degree angle to the crackers.