Trim fat from steak. Cut steak into six serving-size pieces. Lightly coat an unheated large skillet with nonstick cooking spray; heat skillet over medium-high heat. Add steak pieces; cook until brown, turning once. Place meat in a 2 1/2- to 3 1/2-quart slow cooker. Add tomato juice, garlic, and 1/4 cup water.
Cover; cook on low-heat setting for 8 to 9 hours or on high-heat setting for 4 to 4 1/2 hours.
Transfer meat to a serving platter, reserving cooking juices. If desired, slice meat. Cover meat and keep warm.
For gravy, pour cooking juices into a glass measuring cup; skim off fat. Measure juices; add water if necessary to make 1 1/2 cups liquid. In a small saucepan, combine cornstarch and 2 tablespoons cold water; stir in cooking juices. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Stir in horseradish. Season to taste with salt and pepper. Serve meat with gravy.