In a large saucepan, combine first four ingredients. Cook and stir over medium heat until sugar is dissolved. Bring to a rapid boil; boil 5 minutes, stirring constantly. Remove from the heat; stir in marshmallows until melted.
Stir in chocolate chips until melted. Add chocolate bars and chopped chocolate; stir until melted. Fold in vanilla and pecans; mix well. Pour into a greased 15x10x1-in. pan. Chill until firm. Cut into squares.Yield: 5-1/2 pounds.