1998 isuzu box truck 350 motor wont start

Can somene give me advise about this truck. All it does is cranks. So far i put new plugs, wires, cap, rotor, coil, pick up coil, crank sensor, igition module, new igition switch, and a fuel pump it still has no spark or fuel pressure anyone have an idea does any one think it can be the oil pressure switch it has the 3 wires on it