95 maxima misfire code p0306.

I swap sparkplug 5 &6, I swap coilpack 5&6
and still misfire cylinder 6.
Does anybody knows what is wrong, should I Swap injectors too?

You could try to swap injectors, however there could be other issues. Check for rodent damage on injector #6 wires. The main harness that runs along the strut tower is notorious for breaking and causing problems. Unfortunatly Nissan has a problem with those coil packs on those engine's, and even though it says #6 misfire the computer is not always that acurrate for diag. Nissan actually recommends to change all the coil packs at the same time (ouch) and to always run factory s-plugs.