I had a very similar problem on a 4.0l jeep. It turned out to be the pump.
(I know, I know, it's not a JEEP)
Assuming you have no fuel leaks, if you have a fuel pressure gauge to check fuel pressure you can watch the pressure when you first start the engine. It should hold pressure after you shut it off. If the pressure is dropping off you can pinch off the return line from the regulator to the tank so no fuel will get past the regulator and eliminate it in the fuel circuit. NOTE: This may take a while depending on the time it takes for it to hard start. Could be 15 mins or even over night. Just be patient.
If the pressure holds then, regulator is suspect. If not,then more likely a fuel pump. If there was an injector leaking it most likely would flood a single cylinder and misfire badly when you first fire it up (and black smoke). If you have access to a gas analyzer you can look at the readings to see if an injector could be causing the pressure loss since it should be leaking and cause higher emissions.
You could even pinch off the fuel line from the pump to the fuel rail after shut down to see if the pressure bleeds off. If no pressure loss, then the pump is highly suspect. If pressure is lost then a bad injector is certain.
If it turns out to be an injector, then... which one?...you ask. That will take disassembly and inspection to know for sure. You might find puddled fuel in the intake runner of the injector that was leaking or even possibly a runner that is way cleaner than the others or you may ultimately decide to replace them all since they are all of the same age and mileage. Hope something here helps you find your problem or at least leads you in the right direction.
