This is a 2000 Sonoma with Vortec 4300 V6 SFI engine and 70K miles.
Truck runs well, doesn't miss or choke at any speed.
The problem is, once in a while it won't start. It cranks strongly and will
fire when key is released from start position, but not enough to stay
running.
Sounds electrical doesn't it?
It has new battery.
Even when jumped to another vehicle it acts the same.

When amp guage reads 14 volts will not fire at all.
After extended cranking it will start to fire on maybe one cylinder but will
not catch.
Watching the amp guage when cranking, the engine will start to fire at 12
volts and will continue to fire on maybe one cylinder when cranking.

I have primed the carb thinking it wasn't getting fuel, no change.
If it was fuel related I would expect the engine to catch and run until the
prime was burned, no such luck.

Once the engine starts, you can turn it off and it will restart normally.

I have Googled this trouble and read of similar troubles having to do with
fuel pumps and EGR valves and igition module.
None of the other posts indicate that the engine starts with extended
cranking as mine does.

Bill