Preheat oven to 375°F (190°C).
Bring a large pot of salted water to a boil and cook jumbo shells until al dente, approximately 9 to 11 minutes. Drain and rinse with cold water to stop the cooking process.
In a large mixing bowl, combine ricotta cheese, 1 cup of mozzarella, parmesan, egg, minced garlic, parsley, salt, and pepper.
Gently fold the chopped shrimp and lump crab meat into the cheese mixture until evenly distributed.
Spread 1/2 cup of alfredo sauce over the bottom of a 9x13-inch baking dish.
Stuff each cooked shell with approximately 2 tablespoons of the seafood mixture and arrange them in the prepared baking dish.
Pour the remaining alfredo sauce over the shells and sprinkle with the remaining 1 cup of mozzarella cheese.
Cover the dish with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and lightly browned.
Garnish with extra parsley and let rest for 5 minutes before serving.