>>cwwc+(OP)
> When he sold the truck, his buyer hooked it up to a computer that told them the real mileage was around 400,000 miles.
I’m not knowledgeable about odometers at all, but if it’s as easy as “hooking up to a computer” to get the real mileage, why don’t people do that when they buy the trucks?
>>rainco+G5
This comment was not clear. Odometer in car computer can be changed too. There exists special obd command to do this (when you need to replant ECU between engines), but you need to have a password (which is provided with "official" diagnostic computers/tools). If car has no mechanical odometer (most new passenger cars today don't), this is the only way to change odometer values.