Hello. I have a 2013 Grand Caravan SE, with an engine issue no one's able to figure out. I need any help anyone knowledgeable can offer. Misfire on cylinder #5. First, re: fuel delivery; new fuel pump, injector (twice), throttle body, mass air flow sensor, air filter. Replaced camshafts, rockers, lifters, as they were going, camshaft sensors, plugs, coil pack. The problem is that the car, with a new plug, and codes cleared, will run fine for around twenty miles, then it will begin to run roughly, with some hesitation around the 50 - 60 mph range, until I downshift, which temporatily smooths out the engine. The check engine light will come back on. Acceleration is fine, plenty of get up and go, so I'm not thinking it's a cylinder issue. It will run until it hits that twenty mile or so mark, then the car goes south. Any thoughts? Thanks.,