Not really "the truth about the 'Truth'" -- it seemed completely unrelated at the beginning -- but fiction literature was decisive in making me move from the JW mindset, more generally. Actually I think it was particularly helpful because it was fiction and did not threaten my "belief system" directly: switching the fiction mode "on" switched my JW defensive mode "off" so to say.
Mostly French writers first (Giono, Camus, Yourcenar...) -- incidentally, working in English to French translation at Bethel made me sorely conscious of what I had missed about my own language and culture reading only WT 'literature' for years; then Hermann Hesse (Der Steppenwolf, Narziss und Goldmund, Siddhartha) led me to my "crisis of consciousness".
Later on I found that some movies (another kind of fiction, so perhaps not totally off-topic) had probably an even more powerful effect on me.