2006 sierra 5.3 vor tec. Starts for 1 sec and that's it...checked the fuel pressure today and i'm getting 51 after cycling the key a few times and stayed there after a min or two. Truck was sitting for a few months. Checked the air flow and its clean. I can hear the feul pump and doesn't sound heavy. What should i check for? Thnaks

 

Sounds like the anti theft system somehow was triggered, maybe due to sitting and possibly the battery being low or dead. Worth a try