Rough Idline and shaking while accelerating

I am at my wits end. I have a 1998 Exp. 4.6L 4x4. I was having a problem with the truck violently missing causing the truck to shake and jerk. The Check Engine light came on and the code pointed to a misfiring plug. I change the spark plugs, plug wires, both O2 sensors and put fuel injection cleaner in the gas. It then ran fine for about a week then started the same thing again including the same code from the check engine light about a missfiring spark plug. I then replaced the two coil packs thinking that one of those was misfiring. It again ran fine for about a week and has now started up the same thing. I don't know what to try next. Is it still related to the ignition system or should I be looking somewhere else like the fuel filter or EGR valve. I have read several posts with similar issues but with no clear resolution.

Look at the heater hoses . These were bad about leaking down on #4 coil causing it to misfire. What codes did you pull?

Your reply makes sense the code that I pulled said that Plug #4 was misfiring. If the hoses were leaking and I replace them will I have to replase plug and or wire for #4 or will just keeping it from gettting anymore moisture in it help.

Remove the plug and see if there is moisture in the plug well. Dry it out really good and replace the plug. Check the boot really closely for cracks or spark tracking through the boot to the head.

Thanks for the input. I took it to a friend who is a service tech for a Harley Dealer. Him and his coworkers were working on it and he sprayed some Brake Cleaner into the intake and it cleared right up. He seems to think I have a valve or seal that is dried up and the brake cleaner caused it to swell back up and plug the leak. He said it would only be temporary.