I am having the same problem sort of with my 97 sport 4.0. It rough idles and shudders as if it is missing, but i have replaced the plugs( PITA by the way), Wires and Coil pack. While crawling the threads for some answers, I read where the fuel filter might be an issue, I replaced that as well but to no avail. Im not usually a pick and replace kind of guy but this one is really stumping me, cause its not throwing any codes. Either that or my CEL is burnt out lol . I see this is pretty common so i think we should just keep crawling and see what we can find.