The female cop tells the FBI that the "slugs" that killed Paul are embedded in the truck and in a tree. There were no slugs, Layla shot Paul twice with a shotgun.
Sally always shuts her engine down every time she stops. This isn't the way truckers treat the big diesels in their trucks. It takes much more fuel to start an engine like those than it does to just let it run. Another factor is that a shut down and restart also causes excess wear as the engine returns to operating temperature, so starts are kept to a minimum on a trip, with the engine kept running sometimes for days at a time.