02 Chevy Express, 5.7, 139K.  With little warning refuses to start, it will pop and fire a bit sometimes kicking the starter back but will not run.  Sometimes the starter continues to spin disengaged, sometimes the whole thing stops like the battery is dead, but turn key off and on and it cranks again, sometimes it bucks like it's almost trying to run backwards.  

Until it quit it usually would need to crank a little, stop, crank again to start, which was presumed to be a sticky valve letting the fuel drop back.  One afternoon it started hard with some of the bucking, but did start; it seemed to run fine after that but was a little rough waiting at a light.  36 hours later I got this. 

It has new battery (December), $150 Delphi fuel pump, replacement tank, filter (all this week), and the temp sensor is about 8 months old.  I can hear this pump cycle; the tank was seeping fuel so it needed to be changed and I found a fairly new used one at the pick-a-part.  Changed all that, put about 5 gallons of gas in it and cranked it and the same symptoms as before.  I can crank it until the battery is worn down and the most it ran was about 15 seconds at very low RPM.  

And there's no codes in it.  I have a low end scan tool I can look at live data with but I don't see anything abnormal.  

i wonder if it's the regulator (under the upper intake on these so a bear to change) or some electrical issue, maybe the passlock system acting up.  Maybe a ground strap has gone bad.  It's a northeastern vehicle and has pretty heavy rust.  If the regulator is now stuck open could be the fuel just returns to the tank.  I would think an ignition issue wouldn't come on suddenly and just not work - unless the distributor is so broken it cannot stay in time - but I would think that would show in the live data somewhere.  The distributor in these is plastic and they do sometimes wear or break.  

I'm just frustrated and at a loss to figure this one out.