hard to start

2002 chevy venture , hard to start, have to cycle key 2 or 3 times, fuel pressure reg replaced, maf replaced, map replaced, cam and crank sensor replaced, ignition coil replaced fuel filter replaced ,pcv replaced, no problem w pk3, no vacuum leak (smoke test performed) good battery and overall voltage, but fuel pressure only shows 20 psi (switch on ,and running) and as soon i shut down the engine drops to 0 immediately, no gas smell, no shorted ground only one code P0171 b1 lean condition O2 sensors ok...any suggestion?? .