Doug McClure and Steve Clake splitting air time

I really like the Lee J. Cobb first 4 seasons on the show along with Steve Clarke's character of "Steve". However i did notice that during season 2-3 Doug McClure's character "Trampas" rarely shared episodes with Steve Clarke's character. Either Doug was casted in the "credited only" category or Steve was, and during Steve Clarke's run on the show he mostly had more air time than Doug. I've been wondering for some time now whether there was some form of personality conflict between the two actors or due to production costs it may have been too expensive to provide equal casting or billing time for both of the actors especially since James Drury was the highest paid on the show alongside Lee J Cobb. In the nine seasons of The Virginian's run there were consistent situations of actors leaving the show even at the height of popularity ie: Lee J. Cobb, Steve Clarke, Roberta Shore, LQ Jones, Don Quine & David Hartman. And thier stay on the show were never long. And mostly were never explained why they left or were "replaced" on the show, knowing how expensive production costs for the show were it just makes me wonder why Trampas and Steve were rarely casted together.