In a sizeable mixing bowl, thoroughly combine the yellow cake mix and pumpkin puree to achieve a consistent batter.
Transfer the batter into a suitably greased 9x13 baking dish.
Bake the mixture at a temperature of 350 F, adhering to the duration specified on the cake mix packaging, typically ranging from 23-28 minutes.
Once baked, allow the cake to cool for approximately 10 minutes.
Utilize the handle end of a wooden spoon to create uniform holes across the surface of the cake.
Evenly distribute the sweetened condensed milk over the cake, ensuring it permeates the holes and is absorbed by the cake.
Place the cake in a refrigerator and allow it to chill for a duration of 30 minutes.
After the refrigeration period, uniformly apply the Cool Whip on the cake's surface. Subsequently, garnish with Heath bits and an adequate amount of caramel sundae sauce.
For optimal results, refrigerate the cake for an additional 3-4 hours or let it set overnight.