06 5.9 VIN is correct starts and dies after flash

[Twistedshafts]

I am struggling to figure out why this truck will start and die after a flash. The VIN is correct but it acts like it isn't. Trucks runs for a few seconds before shutting off.

[GMPX]

What about with the tune you read out of it, or a 100% known stock tune? (sometimes some of the handheld tuners don't do a true return to stock).

[tylerltr450]

is anti theft on?

[Twistedshafts]

Got it figured out. I wanted to post the results here. Flashed in my tune file and the truck started. After a couple of seconds, it would shut off. Thought I had messed the VIN up but I did not. Tried multiple stock tune files and it did the same thing. Started thinking it had to be a security thing. Found a post on SKIM for people having problems with the key fob. Truck would start and die. This truck does not have a key fob. I called the owner and he said it never had one. I was thinking maybe this was it. The truck wasn't seeing the key fob. I disabled the anti-theft and turned of the DTC for SKIM. Flashed in the new tune file and ran perfectly. Dealer must have shut this off for the previous owner and when I flashed in the new tune file anti-theft was on. If you or your customer don't have a key fob be aware of this situation. Thanks, everyone for the help.