In a large saucepan combine first 4 ingredients. Cook and stir over medium heat until sugar is dissovled. Bring to a rapid boil. Boil for 5 minutes stirring constantly.
Remove from heat and stir in marshmallows until melted. Stir in chocolate chips until melted. Add milk chocolate bars and chocolate squares stirring until melted. Fold in vanilla and pecans and mix well.
Pour into a buttered 15x10x1 inch baking pan. Chill until firm. Cut into squares. Store airtight.