How severe is the misfire, what do the misfire pids indicate, what do you observe (when looking at engine) and feel (when driving)...?
You can also try this:
- check spark using something like
KD2756, want to see a big spark;
- ohm the plug wires from the suspect cylinders, and compare with good cylinders;
- swap coils;
- swap injectors;
- block kit test (checks for presence of combustion gases in cooling system);
- compression and leakdown tests;
Is coolant level staying the same (over a long period of time)...?