Preheat oven to 350°F (175°C) and grease a 9x13 inch baking dish.
In a large bowl, mix cake mix, pumpkin puree, oil, milk, eggs, and pumpkin pie spice until well combined.
Pour the batter into the prepared baking dish and bake for 30-35 minutes or until a toothpick inserted comes out clean.
Let the cake cool for about 10 minutes, then use the handle of a wooden spoon to poke holes all over the top.
Pour the sweetened condensed milk over the cake, letting it soak into the holes. Cool completely.
Spread the whipped topping evenly over the cake. Drizzle with caramel sauce and sprinkle with chopped pecans, if using.
Chill for at least 1 hour before serving.