Truckzilla
From Super-wiki
"Truckzilla" is the pet name given by fans to John's Truck.
It was first coined by LJ user disanddat in a thread in the papawinchester LJ community on the 31 of march 2006. Full thread here
The input for the name came from a TWP's Supernatural episodes recap: "...and Daddy walks off to get in his Truckosaurus Metallitruck." (the link to that recap now points at a 404 error)
John's truck is a 1986 GMC Sierra Grande.