It is established when her character is introduced that Amber was in the Marines. Later, another character says he read about her and her time at West Point. A Marine would not have attended West Point, that is only for US Army officers. A Marine would have attended the US Naval Academy.
When Kimberly Caldwell calls her agent he complains that it's 4am in Los Angeles. She's driving in West Virginia, and the shadow the car casts indicates the sun is directly overhead, so it's about midday (the shadow sits under the car in every shot). However, if it's 4am in LA, it should be 7am in West Virginia, so the sun should cast long shadows.
When Kimberly is sliced in half and the hillbillies drag her two halves away, the body parts they are dragging don't bleed at all. Seconds after being sliced in half, all of the blood from the arms, legs and other parts of the body would be flowing out of the open side.
When Dale escapes and fights with the mutant, shooting him with the shotgun, he then runs to Mara and turns her over, realizing that she's dead. In the closeup scenes with Mara, her chest moves like she is breathing, even though she supposed to be dead.