My 5.3L Tahoe LT vin Z starts very smoothly but the rpm goes to zero within 3 seconds. Most cold starts will not do that but when its at temperature and I allow enough time for the temperature to come down half way then it will choke out. I replaced the PCV valve twice but saw no change. What should I be looking for? I just replaced the plugs and wires thinking it would help too but no improvement there.

 

I'd be looking at the fuel pump, fuel pump relay, test your fuel pressure regulator PSI. Might also be crankshaft positioning sensor, EGR valve, or the even the MAF. Sometimes these things dont through a code, which makes it harder to diagnosis the issue..

 

with oil can, check your fuel pressure