In a large bowl, combine brown sugar, white sugar, salt, and cinnamon with a fork. Add in corn syrup, vanilla extract, eggs, and 1/2 cup melted and cooled butter. Mix well. Fold in 1 cup of pecans until well-incorporated.
Pour mixture into a greased 9×13″ pan. Over the top of the mixture, evenly spread cake mix. Top with remaining pecans (1 cup) evenly. Pour 1 1/2 cups butter over the top of the dish, until most of the cake mix is moistened.