Combine gelatin with Dr Pepper. Set aside. Combine salt, 1/2 cup sugar and beaten egg yolks in top of double boiler. Stir in gelatin mixture. Cook and stir over hot water until slightly thickened. Add lemon juice. Chill until partially set, stirring occasionally. Beat egg whites until foamy. Add 1/4 cup sugar gradually, beating until stiff peaks are formed. Fold in gelatin mixture; then fold in peaches. Chill until mixture mounds when dropped from a spoon. Pour into cold pie shell. Chill until firm. Serve plain or garnished with whipped cream and additional sliced peaches.