if what you have done hasnt solved the missfire, take it for a drive, do a few ks and then pull the plugs out one by one and check them
if they are being fired properly they should be blackened
if you find one that looks like its brand new or not as used looking as the others, then chances are the coil pack for that cylinder has flogged out
you will need to replace that one
thats what solved my misfire problem