Prepare the Crust: Preheat oven to 350°F (175°C). Mix pecans, melted butter, and graham cracker crumbs. Press evenly into the bottom of a 9×13-inch baking dish. Bake for 10 minutes, then let cool.
Make Cream Cheese Layer: Beat cream cheese, powdered sugar, and vanilla extract until smooth. Spread evenly over the cooled pecan crust.
Pumpkin Pudding Layer: In a bowl, mix pumpkin puree, instant pudding mix, and pumpkin pie spice until smooth. Spread evenly over the cream cheese layer.
Top with Cool Whip: Spread Cool Whip evenly over the pumpkin pudding layer.
Chill: Refrigerate for at least 2 hours (or overnight) to allow the layers to set.
