In a medium bowl, mix soy sauce, light brown sugar, distilled white vinegar, garlic powder, seasoned salt, garlic pepper seasoning, and lemon-lime flavored carbonated beverage. Reserve about 1/2 cup of this marinade for basting. Place steak in a large resealable plastic bag. Cover with the remaining marinade, and seal. Refrigerate for 8 hours, or overnight.
Bring a saucepan of water to a boil. Add green peppers, and cook for 1 minute, just to blanch. Drain, and set aside.
Preheat grill for high heat. Thread steak, green peppers, mushrooms, tomatoes, and pineapple onto skewers in an alternating fashion. Discard marinade and the bag.
Lightly oil the grill grate. Cook kabobs on the prepared grill for 10 minutes, or to desired doneness. Baste frequently with reserved marinade during the last 5 minutes of cooking.