Why isTruck Idling rough runs rich Has miss and no power + shows po300 code

Obviously the 4.3L .... With fuel pressure gauge hooked up... Turn key on & note pressure... Turn key off & note pressure.. If drops off more than 10 psi... *Suspect fuel spider under intake plenum* Crankshaft position re-learn proceedure using scan tool WILL be needed since you've replaced the crank sensor!.. Although code indicates 'random' misfire... Strongly suggest using proper scanner with live data to monitor engine misfire to determine exactly WHICH cylinder(s) actually mis-firing before proceeding.... Then you know exactly where to look should intake plenum need to be removed.... STOP GUESSING AT IT!!

best thing to do would be a compression test, not sure wut ur mileage is, could be leaky head gasket, idk if ur fuel injection has the "poppet valves" , that could be an issue as well. also mayb check ur coolant temp sensor, and make sure ur "EGR" or exhaust gas re-circulation valve is not half clogged w carbon. smell ur coolant, does it smell like fuel? idk need more info to go on.