Been listening (for the third time in 5 years) to Robert Parker's Virgil Cole and Everett Hitch books on audio. The first was Appaloosa, which the movie was based on. There are a total of ten, though only the first four were actually written by Parker. The rest were written under agreement with the Parker estate by Robert Knott. He does a good job of consistency in style and content. I read somewhere that much of Knott's books in the series were based on notes and outlines left by Parker.
Parker was a prolific novelist, and authored the Jesse Stone police series made popular by Tom Selleck.