Plot hole: This huge demon monster flies around and is seen by at least 30 people, and the day after this demon kills all these people. Everyone just goes on with their daily life. Where the hell is the FBI and the National Guard, this thing just killed 10 people and there's no search the next day for this demon that killed about 5 police officers?
Plot hole: Since when do hell-born freaks have an intuitive knowledge of mechanics? And where did he get the turbo engines and various add-ons needed to reach such high speeds? It's a small rural area and it would look pretty odd if he just strolled into an auto shop and piled the stuff into a trolley.
Plot hole: The whole point of Darry going down the pipe near the beginning was because he couldn't see the bottom of the pipe. However, Trish can make out his shock when he notices the body. Darry's flashlight is not providing the light in this scene as the light is coming from the tunnel.