I think there might be something darker at work here. The more I think about the Truckster, and the impact it had on the Griswold family, the more I think it had some sort of malevolent presence that, while more subtle than that displayed by the killer car in Christine, was no less real. Perhaps the better example would be the Ring of Power that Frodo carries in The Lord of the Rings. Like the Ring, the Truckster was a talisman of doom that brought ill fortune and slowly but inexorably put its bearer under its twisted influence.
"Vacation" was a great movie - a classic of the 80's, no doubt.