1996 Silverado 5.7 litre P0300

I have a 1996 silverado with a 5.7 litre engine that was purchased used (no idea with respect to previous mtx history form the list of replaced parts from problems I found it appears this truck was not cared for properly) , that is giving me a random multiple misfire code I have already replaced the injection spider, fuel pressure regulator, fuel pump, fuel filter, spark plugs, wires, cap, rotor and all four 02 sensors. in addition to the L/H head due to a crack, plenum seals and gaskets, and sprayed carb and choke cleaner looking for leaks none detected. For a while i was getting Po102 code but changed the connector to the MAF sensor and that has stopped. now I am getting the P0300 random multiple misfire code The only thing I have not changed in the ignition system is the coil and the ignition control module in the distributor. Is it known for these components to cause this issue? The truck starts and idles fine and I have driven up to 29 miles before I get this code. Any help or direction would be greatly appreciated.

 

try some Chevron 65740 Techron Concentrate Plus Fuel System Cleaner.works great.may have some carbon on valves.this is a difficullt code to diagnose.....really need to look at freeze frame data to see when code set and at what load/rpm and also look at missfire counters on an enhanced scan tool.fuel trims short and long term are important information also.you dont notice any rougness/missfire?Before i bought a smoke machine I used propane and ran a vacuum line from bottle and ran along gaskets and listened for rpm change and even monitored 02 voltage on a scan tool.

 

I would be doing a fuel pressure test as well. Have seen multiple missfire code caused by lack of fuel pressure, obviously due to lack of sufficient fuel supply.