Ok I'm having a problem with a random miss in the number 6 cylinder on my 3.9L I've changed the injector (even swapped injectors on other cylinders), changed the spark plug (even swapped spark plugs on other cylinders), tested the spark plug wires, and changed the distributor cap. Now the weird thing is, the one mechanic I took it to couldn't figure out the problem. He said the random misfire only happens at idle. Not when actually driving the truck. What else could be causing the problem?