Miss fire on cylender 4 and 6 what would cause this???

What is your question?

I have a 97 astro or miss fire on 4 and 6. I have changed the plugs wires cap and button. But still have a miss fire. Sometimes it runs good and smooth and other times rough. On idle it is smooth but when it runs ruff it can be at take off or when cruise is set. On the passenger side above the spark plugs there is the same nasty sludge as in my coolent. No milky or froth in oil I do use coolent. And also no sweet smell or white smoke coming from the muffler. What could be my issue?????