Preheat oven to 350°F (175°C). Grease a 13×9-inch pan.
In a large bowl, mix the cake mix, pumpkin puree, water, oil, eggs, pumpkin pie spice, and cinnamon until well combined. Pour into prepared pan.
Bake for 26–33 minutes, or until a toothpick inserted comes out clean. Cool for 30 minutes.
Meanwhile, make the caramel: In a saucepan, combine cream, brown sugar, and butter. Bring to a boil, then reduce to simmer for 12–15 minutes, stirring often. Remove from heat and stir in vanilla. Reserve ¼ cup plus 2 tablespoons for whipped cream and garnish.
Poke the cake all over with the handle of a wooden spoon. Slowly pour sweetened condensed milk over the cake, letting it soak in. Drizzle most of the caramel topping into the holes. Cool completely.
Whip the cold cream until soft peaks form. Add reserved caramel and beat until stiff peaks hold. Spread over cooled cake.
Top with toasted pecans and drizzle with remaining caramel before serving.