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Looking for the title of a book likely published around 1980-1995 or so where the main character drives an old (1950s or 1960) pickup truck down a time travel "road" that others travel as well. He is chased throughout the story by a dragon of some sort I think. Cover showed the back of the old truck and maybe guns or a dragon tail. Main characters were an old or older man I think, traveling with a younger man or boy. Not sure about that. The opening sequence has the older character stopped by some sort of time travel road policing agents as he is trying to take guns back to Sparta/Troy? to help them win a battle.