Heat oil in a large skillet over medium heat. Sauté onion, bell pepper, celery and garlic until tender, approximately 15 minutes. Stir continuously. While vegetables are cooking, blend stock and flour together until smooth and lumps are completely gone. Use strainer, if necessary. Add tomatoes, all-purpose seasoning and flour/stock mixture to the vegetables. Stir. Add okra and bring to a boil. Reduce to a simmer, cover and cook until okra is tender, approximately 20 minutes. Add shrimp and cook for an additional 5 minutes, until shrimp are completely cooked. Add salt and pepper to taste.Serve over cooked rice.