HARD TO BELIEVE: Astounding real life stories! Courageous undercover grandmas! Heroic life-saving dogs! Yes, it's amazing but true: NBC has another "reality" concept for your consideration. This time its "Against All Odds," which dramatizes the lives of regular folks who have triumphed over adversity. Lindsay Wagner and Everett McGill are the hosts. The one-hour special, made up of two back-to-back episodes, will air at 6 p.m. Sunday on Channel 5. Half-hour installments of "Against All Odds," from the producers of NBC's hit "Unsolved Mysteries," will air at 6:30 p.m. on the following two Sundays. - Ginny Holbert