The code P0300 is something that should be shared in the beginning. Random/multiple misfire code. If feels exactly like it did before ignition parts were installed, I doubt the problem is them but yes, like
@Keeper and
@Das Hatt said, recheck your work. If you had crossed wires before and installed new the same way, that could explain. personally, I am a big fan of knowing the compression. Remove plugs and inspect how each looks and make sure to lay out in cylinder order and do a compression test with all plugs out. Post results. Check for vacuum leaks as well.
