I was out running errands today, 95 degrees, A/C on pulling out of parking lot, when engine just shut off QUICKLY. Tried to restart, turns over fine, but no fire. I installed the 6th fuel filter 1,000 miles ago. I now have 60,000 miles on truck. Since it happened so quickly, could it be something electrical? it is now with the local dealer. I think I miss Onstar on days like today.

Did you check the ignition fuse?

I had mine die and it was a broke wire in the loom on the drivers side of engine.It blew the ecm fuse.

Mine did this once and it was the batteries. Did the tranny act funny when it was running?

mine did the same, 1st time it was the FICM(fuel injection control module) and now its the wiring harness to the FICM that apparently has a cut(s) in the wiring shorting it out cutting off the engine

I also had this happen but mine was a bare wire shorting out the edu fuse to the fuel injectors. Look closely at wiring harnesses.
Good luck.

I heard of a bad ground wire on the frame causing silly things like this too!

make sure the water bleeder valve on the bottom of the fuel filter is still on/not leaking...