i have a 96 deville runs great but every few days it will start thenn shut right back off. I k now it has to do with the vats shutting the injectors off, but it has been to the dealer numerous times they have replaced the cluster and the ignition switch but it still does it what controls the vats on this car and sends the message from the ignition switch to the pcm that this is a valid key. Please help any ideas this has been going on for almost a year.

 

Stupid it may sound, but have they replaced the ignition key(s)? The embedded resistor pellet may have gotten worn out.

 

both sets of keys have the same result we have thought of that, that is when we got the second key made for it.

 

Right. You have the Pass-KeyII security system, or at least that was the name for it in 1997, and it wouldn't even let you start the car when a non-matching key is detected. Normally, it wouldn't even crank because the starter is disabled. That the car starts running indicates that, indeed, the injectors shut down. This latter event depends on the outcome of a "dialog" between the IPC aqnd PCM. The PCM monitors the Class 2 serial data line for the fuel enable message from the IPC. So either the IPC errorneously does not send this message or the PCM does not receive it (or "thinks" it's not there), and it locks down the injectors.
You have replaced almost every component of the system except the PCM and the serial cables. I'd go for the cables first...