One thought that occurred to me while reading was that, as BH said, an injector could be leaking down, letting raw fuel into a cylinder or cylinders of whichever injector or injectors are leaking. Also, the fuel pump check valve or pressure regulator could be leaking fuel back into the tank. Both scenarios result in emptying or partially emptying of the fuel rail.
Since you had just replaced the injectors, it would be total coincidence for the fuel pump area to start leaking down - as you suggested, more likely an injector.
The way to tell which scenario it is is when it's having trouble starting, when it finally does fire up, do you smell raw gas fumes out the exhaust? If yes, then injector leaking fuel into a cylinder (flooding the leaking cylinder(s)) and air in fuel rail (fuel starvation in the other cylinders). If no, more likely the fuel pump check valve or pressure regulator causing air in fuel rail (no flooding, but fuel starvation in all cylinders). (Either scenario would result in sputtering for a few seconds right after it does start while the air in the rail works its way out.)
Another point: When it has trouble starting, turn the key to Off for a couple of seconds, then to Run for a couple of seconds, then repeat. (Cycling the key like that causes the fuel pump to run for a second or two and then stop - the PCM doesn't run the fuel pump again until it detects that the engine is actually running. The purpose of the cycling is to get enough fuel back up into the rail to partially fill it back up and pressurize it)
After at least 2 cycles of that, *then* go to Start. If it does fire up (even if it sputters after starting), that would pretty much prove low fuel in the rail (due to either injector, fuel pump check valve, or fuel pump pressure regulator leak down). If it doesn't start up after that, then that's likely not the problem.
Originally Posted by BH199
...And why one rocker arm would be different from all the others and give reason to replace a camshaft says that there's more to that story...
There may indeed be more to the story, but I have vague recollection of reading a few threads discussing it not being uncommon for the 3.2/3.5 cam and rockers on one side (forget whether it's always driver or passenger side) needing replacing. I believe someone posted experiencing this and also, being a frequenter of salvage yards, that they had observed the same thing on many engines seen in salvage yards - one side good, other side bad, and always the same side bad. Maybe someone else recalls what I'm talking about, 'cause I sure don't know.