When Ed Landers turned around to shoot uphill at James Wylie who was coming in behind him, his gun went off before he was turned halfway around, when it was still pointed at the ground.
When Wylie is showing off in the stagecoach by making a deck of cards fly between his hands, it's obvious that he's using an accordion deck and not a real deck of cards.
After the stage leaves Cheyenne at night, the darkened view of Cheyenne in the distance is the same as the distant view of Laramie used early in the film.
In a few shots during the stage coach chases, there are tracks on the ground obviously made by pneumatic tires, not wagon wheels.
During the second stagecoach robbery, the second member of the gang to be shot grabs his chest before the gunshot is heard.
When Ann is telling Wylie to get out of the bathtub, a shadow of the boom microphone can be seen to dip down onto, then move off of the room partition between them.