Most missfires are spark plug or coil related ..... I would start with spark plugs and a check of the ignition coils for signs of arching or burning
Why would all 3 spark plugs (2,4, & 6) go out simultaneously on one side of the engine though? I've never heard of 3 plugs or coils (they are mounted on the plug) going out at the same time
they have been know to, one easy way to tell if there is no damage is to move the coils to 1 3 and 5 and see if the miss fires move ...if they do you just solved your issue.
it could be a wireing issue to the injectores it could be a clogged injector rail it could be a head or intake gasket leak, some basic trouble shooting will be required to pinpoint the issue
its very unlikley, i would check the plugs and coiuls first
you can try a fuel system treatment like chevron techtron and see if it clears it up