1999 Z71 5.3 Auto. Just bought this truck today and now this! I must have started it ten times when I was looking the truck over. Then after I got home this started. I tried both keys and it will not start. UGGHHH It cranks and fires and the tach goes to about 700rpm then immediately it dies. The security light then flashes for a bit. From what I am gathering this appears to be VATS related. Any help would be GREATLY appreciated. EDIT: I waited about ten minutes and just checked the 'SECURITY' light is still flashing.