Engine shuts off when transmission is shifted into gear?

Okay, you can start it up and it runs fine but it shuts off if you put it in gear, does it matter which gear or does it shut off as soon as you move the lever out of park? If you shift it to neutral, will it start? Does it have a factory anti-theft or remote start or an aftermarket remote start or alarm on it?

Thank you. The reason I asked is that many remote start and aftermarket alarm systems are built so that you can start the engines but if the key isn't in the ignition it shuts off the engine if you try to shift out of park. The OE PASS Key theft system doesn't work that way though. I suspect it's related to the park neutral shift sensor that tells the ECM if the truck is in park or neutral and when you shift one of the 4 connections is bad. Try to start it in neutral and see if it will start and then what it does if you try to shift it. Is the check engine light on?