Preheat oven to 350 degrees. Cook 1 16 oz. package jumbo shell pasta until just tender. Drain, then rinse with cold water to cool so you can handle the pasta while stuffing.
Meanwhile, in a large bowl, combine 1 16 oz. container ricotta cheese, 1 cup mozzarella, 2 cups shredded mozzarella cheese, 3 tablespoons sour cream, 1/3 cup dried bread crumbs, 1 teaspoon dried oregano, 1 teaspoon dried basil, and Salt and pepper to taste; mix well.
Spray a 9×13 inch baking dish with non-stick cooking spray and cover bottom of dish with a thin layer of marinara sauce.
Fill shells with cheese mixture and place in dish; cover with 2-3 cups marinara sauce. Sprinkle remaining mozzarella cheese on top of sauce.
Bake, covered, for about 30-40 minutes or until cheese is melted and sauce starts bubbling. Uncover and bake an additional 5-10 minutes.