In a medium bowl, combine the graham cracker crumbs, butter and sugar. Press the crumb mixture on the bottom and up the sides of a 9-inch pie plate. Place the crust-lined pan in the refrigerator or freezer until the crust is very firm.
PREPARE THE 1st LAYER:
In a large bowl, whisk together the cream cheese milk and sugar until smooth (you can also use an electric hand mixer for this). Gently stir in 1½ cups Cool Whip. Spread the cream cheese layer evenly on the bottom of the prepared crust.
PREPARE THE 2nd LAYER:
In a second bowl, whisk together the pumpkin, pudding mixes, milk and spices. Whisk until well blended (the mixture will be thick). Spread the pumpkin layer over the cream cheese layer.
SERVE:
Refrigerate for 4 hours, or until well-set. Serve slices topped with more Cool Whip. Garnish with a sprinkle of cinnamon, if desired.