6 medium potatoes, peeled and cut into chunks
1-1/4 cups chopped celery
3/4 cup chopped onion
1/2 cup butter, cubed
6 cups unseasoned stuffing cubes
1 teaspoon poultry seasoning
1/4 teaspoon rubbed sage
1 cup chicken broth
4 cups cubed cooked turkey
2 cans (10-3/4 ounces each) condensed cream of chicken soup, undiluted
1 teaspoon garlic powder
3/4 cup sour cream, divided
4 ounces cream cheese, softened
1/2 teaspoon pepper
1/4 teaspoon salt
1-1/2 cups (6 ounces) shredded cheddar cheese