Re: When does one truck become another?
Check with the DMV - they'll have a procedure for this. As was already mentioned, there are guys salvaging totaled cars and building street rods and other customs using a frame from one year, the driveline from another, and a body from yet another, and in some cases they don't have proper title for any of it. I'm sure there's a way to get it done but it may be more hassle than it's worth depending on your state's requirements. No doubt the process will involve an inspection by the state.
It occurs to me that some may not know how and why VIN switching takes place. First, you buy a legally registered beater. All you're intersted in is the clear title and the VIN plate. Next, you steal a nice but similar vehicle and place the VIN from your legal vehicle onto the nice one. You trash the remains of your legal vehicle - usually through a buddy at a car crushing / metal recycling facility and the stolen vehicle becomes the legal one.
I saw a report on the local news about a month ago about a guy who bought a 4 year old Jeep Grand Cherokee at a dealership. Somehow it was found to be a VIN switched stolen vehicle. Now of course everyone involved in the history of the truck is pointing fingers at everyone else and the buyer / current owner is making payments on a truck that has been seized as stolen property.
Bummer to be him.