By Shawn Childs But how will change at QB affect Pittsburgh’s pass catchers? For the first time since 2004, the Pittsburgh Steelers will open the season without Ben Roethlisberger behind center. Mitchell Trubisky expects to start at quarterback, while Kenny Pickett and Mason Rudolph hope to outplay him in training camp. Najee Harris had a tremendous rookie season, but his high production in yards (1,647) came from volume of touches (381), not impact plays (3.9 yards per catch and 6.3 yards per catch). Both Diontae Johnson and Chase Claypool have flashes of exceptional play while needing to imp…