Hi David
as its common to all cylinders, possible fuel pump or fuel pump pressure regulator
if the fuel pressure low, you could check with a gauge like I think you have, but you could try clamping the return line off slightly to get your fuel pressure up to your 55psi
with say some mole grips and then drive it, could be something as simple as the fuel pressure regulator, if you cant achieve the 55psi with clamping the return hose, it could be the fuel pump
it has to be something common to all cylinders, I think there's also a fuel pump ecu, that lowers the voltage to the fuel pump when idling, could be this, some people hot wire the fuel pump to get more power as fuel pressure will be raised, hot wiring is just basically bypassing the ecu/fuel pump control unit, with a ignition supply
common fault with running lean is usually air leaks, split hoses, inlet manifold gaskets etc, but you said you have checked this, you could try some easy start around the hoses, inlet manifold area, if theres a leak, it will suck the easy start in and the revs will raise on idle
could also be airflow/maff sensor, this also can effect mixture of engine
cheers
Joe