Rinse turkey in cold water, pat dry. Remove neck, wing tips, and giblets, and simmer in a small amount of water to make broth (about 2 cups). Melt butter or margarine and saute onions and celery until tender but not brown, cool. Combine bread cubes, salt, pepper, thyme, and parsley. Add sauteed vegetables and toss lightly. Add beaten egg, 1/2 cup Dr Pepper, and broth. Spoon about 1 cup of the stuffing into the neck cavity. Fasten skin to back with skewer. Spoon stuffing into body cavity (do not pack), close body cavity by skewering skin together and lacing it closed with a heavy string. Tie drumsticks to the tail. Place turker in roaster or pan breast side up and roast at 325°F for about 3 hours or until done. Bast frequently, first pouring from the bottle of Dr pepper, slowly over the bird. When all is poured, baste from the liquid in the pan, spooning over the bird at frequent intervals.