Season 4 will be the final season of Preacher. Seth Rogan confirmed this via a tweet on April 8, 2019. Season 4 will begin on August 4, 2019.
While inside the University of the Grail, Featherstone is talking to Cassidy and we see the year the university was established. MCMLXV or 1965.
God states that Diet Dr Pepper is "one of my greatest creations".