Preheat oven to 350°F and grease a 9x13-inch baking dish.
In a large bowl, mix together spice cake mix, pumpkin puree, milk, oil, eggs, and pumpkin pie spice until smooth.
Pour the batter into the prepared dish and bake for 30-35 minutes, or until a toothpick inserted comes out clean.
Let the cake cool completely. Using a fork, poke holes all over the cake.
Whisk together sweetened condensed milk, evaporated milk, and whole milk. Pour slowly over the cooled cake.
Refrigerate the cake for at least 2 hours to let it soak.
Whip heavy cream, powdered sugar, and vanilla until soft peaks form. Spread over chilled cake.
Dust with cinnamon before serving.