Hiero’s Journey may fit the bill. Published in 1973 by Chilton Books, it’s the story of a post-apocalyptic North America. 5000 years after a nuclear war called The Death a priest Per Hiero Desteen (a member of trained killer priests sent out across North America to battle mutants) is sent out to discover a secret from the past to help fight the Unclean; something called a ‘computer’.
Read a review here:
http://lit.coldfusionvideo.com/hieros-journey-by-sterling-e-lanier/
Trivia: Back in the 70s I read in Variety that a certain movie producer was looking at vehicles to produce in to a science fiction movie. Hiero’s Journey was mentioned in the article. This eventually was either dropped in favor of, or was reworked in to the more familiar Star Wars (I don’t remember which). That was the gist and it would take a bit of digging to find that article again.