3406e low power

Look into replacing the fuel transfer pump on the front of the engine. It will cause a power issue without showing up on a diagnostic. This is what the one reply is referring to with shimming the spring. You remove the bolt in the side of the transfer pump and pull out the spring and shaft. A lot of guys take a screw driver and cut it to length (happens to be the right diameter) and remove the spring completely. I have a 6nz and a dash fuel pressure gauge, changed the pump with a new one and pressure rose to 100 psi from 72 psi