Line the bottom of a greased 11x7-in. dish with half of the graham crackers; set aside. In a 2-qt. microwave-safe bowl, combine the crumbs, sugars, butter and milk. Microwave, uncovered, on high for 45 seconds; stir. Microwave on high 1-1/2 to 2 minutes longer. Immediately pour half over crackers in prepared pan. Top with the remaining graham crackers; spread with remaining sugar mixture., In a small microwave-safe bowl, heat chocolate chips and peanut butter, uncovered, on high for 30-45 seconds or until chips are melted. Stir until smooth and blended. Spread evenly over bars. Cover and refrigerate for 1-1/2 hours before cutting.