Drain the pineapple juice into a slow cooker, reserving the pineapple chunks. Place the beef, onions, beef broth, 3 tablespoons red wine vinegar, garlic, seasoned salt, paprika, and black pepper into the slow cooker with the juice. Mix well, cover, and cook on Low until the beef is tender, 6 to 6 1/2 hours.
Increase the setting to High and stir in green bell pepper, red bell pepper, and brown sugar. In a small bowl, mix together the cornstarch, soy sauce, and 2 tablespoons red wine vinegar until smooth; stir the mixture into the slow cooker, blending well. Cover and cook for 1 more hour. Just before serving, lightly stir in the tomatoes and reserved pineapple chunks.
