Place pork chops in a large heavy-duty, zip-top plastic bag. Combine soy sauce, molasses, and garlic powder; stir well, and pour over pork chops. Seal bag; turn bag to coat chops. Marinate in refrigerator 4 to 8 hours, turning occasionally.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Remove pork chops from marinade, discarding marinade. Place pork chops on rack; grill, covered, 5 minutes on each side or until meat is done. Remove from grill, and keep warm.
Combine mayonnaise and remaining 4 ingredients in a small saucepan. Cook over low heat, stirring constantly, until thoroughly heated. Spoon horseradish sauce evenly over pork chops.