Preheat the oven to 350°F. Spray a 13x9-inch baking dish with nonstick spray.
MAKE THE CRUST:
In a medium bowl, stir together the flour, pecans and butter. Press the mixture into the prepared baking dish in a thin layer, patting it evenly into all corners. Bake until set, about 20 minutes. Remove from the oven and let cool for about 30 minutes.
MAKE THE LAYERS:
In a medium bowl, use an electric mixer to beat the cream cheese for about 2 minutes- until it is very creamy. Gradually mix in the powdered sugar, beating until well-blended- about 1 minute. Fold in 1 cup of the Cool Whip. Spread the mixture evenly over the cooled crust.
In a large bowl, whisk together the milk and the chocolate and vanilla pudding mixes until well combined. Let stand until slightly set- about 10 minutes. Pour the pudding mixture over the cream cheese layer and spread to evenly cover; spread the remaining Cool Whip on top. Drizzle with chocolate syrup. Cover and chill at least 2 hours and up to 8 hours.