Divide popcorn and pecans between two 13x9" cake pans; set aside. In large heavy-bottomed saucepan, combine brown sugar, butter, corn syrup and salt. Bring to a boil over medium-high heat, stirring occasionally; boil and stir for 5 min. Stir in soda and chocolate until chocolate is melted. Quickly pour ½ of chocolate-caramel mixture over each pan of popcorn and pecans, tossing to evenly coat. Bake in a preheated 250° oven for 1 hr., stirring every 15 min. Cool and store in an airtight container or zipper-closure food storage bags for up to 1 week.