starts and dies

[RJC]

Hello, be awhile,

I have a 1999 Silverado with 6.0.

It starts rite up then dies after 2 seconds. This is what I've done so far.

Changed fuel pump, and filter, 60 ps1 on fuel rail. Locksmith replaced ignition, No chip on key but its in ignition, checked relays, I've unplugged map MAP sensor, I've been told that it maybe the vats security system and that's why ignition got changed.
Ran scan tool and no codes found.

I hate to keep changing out parts. would crank or cam position sensor be a posibble?

Any help greatly appreciated