I have a 2002 4.2. I'm getting an intermittent problem. It will drive down the road just fine. Then it's like a cylinder or two has dropped out. It will go away after a little bit or if I turn off the ignition and start it right away. I get a P0353 code. I've changed the plugs, wires and coil pack. I see no corroded wiring. I've also tried wiggling wires as it is acting up. I gave up and took it to a garage and they could find no problem, they cleared the code and it's acting up again. it happens about once per drive.
Mine acts like that when a coil is going out, it will act up for a while then just quit altogether. If you can catch it when it is acting up unplug the wires one by one and see if it changes the motor speed, if the speed does not change those plugs were not firing. Sorry i could not be more help.