Crank no start
 

I have a 2011 Silverado work truck. Recently had a low miled 6.2 swapped in for the high mileage 6.2.

Truck runs great. No check engine light.

However it it will randomly not start. Was coming back from a long trip, and stopped for lunch. Truck would crank but it would not start. I waited about an hour and it fired back up.

This has happened about 6 other times and it's becoming a reliability problem.

What can this be? Crank sensor? I don't know any input would be greatly appreciated.

Only mods I have is long tubes. No Vats. No flashing security light. Tuned all O2s off and that's about it. Not a fuel problem since I have a fuel gauge hooked up and I can see there is fuel pressure in the rails.