You are not suppose to keep the pace, it's unauthentic.
Formal parade or inspection, basically anything formal would make sense. But this was just an ordinary march....let see...oh yeah all the way from Atlanta,GA to Bentonville, North Carolina, which explains why men are out of step or carrying ridiclous items. They're basically on the move. Another factor you should note, this was western boys, Sherman's boys, the wild boys from the west, Sherman doesnt care for regulation as long you kill dem rebs.