Combine soy sauce, brown sugar, vinegar, garlic powder, seasoned salt, garlic-pepper seasoning and soda in a medium bowl; mix well and set aside. Arrange steak in a large plastic zipping bag. Reserve 1/2 cup coy sauce mixture for basting; pour remaining in bag and seal. Refrigerate 8 hours or overnight.
Thread steak, peppers, mushrooms and tomatoes alternately onto skewers. Lightly grease cold grill rack. Grill kabobs over high heat (400 to 500°) for 10 minutes, or to desired doneness. Baste frequently with reserved marinade during the last 5 minutes of cooking.