What is the main conflict in The Executioner's Song by Norman Mailer?

Norman Mailer's Executioner's Song is many things, and its status between the realms of fiction and non-fiction makes it difficult to define. It is not non-fiction, notwithstanding the author's claim in his Afterword. The Pulitzer Prize Committee recognized Mailer's work as a "...thoroughly imagined work of fiction." This novel is not a work of non-fiction, but it is also not wholly a work of fiction. The book's form causes us to examine the line between reality and perception. What is the truth? How is truth colored by the telling of it, whether through a novel or through the rules of a trial? Are the points of view about Gilmore that Mailer describes "truth" in any way?