Sorry for digging up such an old thread.

I joined just to reply to this and I hope that my post will help others with the P0340 code.

I replaced both camshaft position sensors and the alternator today after reading many posts and still the code would reappear almost instantly after starting the truck. I cleared the code many times and still the code would come back after starting, shutting off and restarting. So I got upset and started to look at the wiring for what seems like the hundredth time and noticed that the harness that come off the PCM connector closest to the passenger side fender was routed under AC line, well turns out that about four wires within the bundle had the casing chaffed and melted away. For a quick fix due to the darkness and poor flashlight I wrapped each wire with some tape while the battery was disconnected and magically the problem has gone away.

Please inspect this wire harness if your problem continues and you too may find that this is where all your troubles are beginning.

Good luck and hope this helps someone