How do you know for sure you have a miss on #3and #4?Did you do whats called a power balance test?This is where you pull the plug wires one at a time with the engine running and the rpms will decrease and you can hear the engine go down....they all should sound the same when you do it.If one or more cylinders don't pull the engine down then theres a problem with that cyl.A good example is a cyl. with a badly burnt valve will not change at all when you pull the wire off for it isn't providing anything to the running engine and will have very low compression if any.I realize you probably already know this but am making sure......
Take care...........Gerald
