LBZ starts, stalls won't start until it sits for a few hours

[duramaxdon]

I have an 06 LBZ that will start first thing in the morning, run for about 2-3 sec. and then dies. It won't restart no matter how much I crank. Priming the fuel filter doesn't help. Still won't start. But once it sits for a few hours it will start and run for 2-3 sec.
Not throwing any codes. Shop put fresh fuel with electric pump to bypass fuel tank. Truck does the exact same thing.