I have a 2005 Pasifica with the 3.5 that threw a P0300 and P0302 misfire code which i know one is a general and the other is for cylinder 2. It has a rough idle and very sluggish. At 45mph cruising the engine will chug until you either give it more gas to accelerate or let off completely. Also once you try to get to highway speed around 55mph the engine light will start to flash (i cleared the codes) and it will max out at 60mph with the pedal to the floor. I had it apart today and checked the plugs which were pretty much shot so i replaced them. Also i cleaned and checked the EGR valve by spraying carb cleaner in it to see if it was stuck open at all and no fluid came through. The problem is still there but now the car will idle good and has a lot more get up and go at low speed. I am at a loss of what to try next but one thing i was thinking is that it might actually be a coil or maybe a clogged CAT. Anyone have any suggestions or run across this issue before.

 

Try swapping the coils boot and all to a new cyl visa versa and see if you get any trouble codes i have done this and it followed the cyl which was cyl 5 so replaced the coil on 5
now you said you changed the plugs these cars have a good look at the plastic upper intake manifold to make sure you didnt place the manifold wrong this will cause leaks (forsure) and just double check all your connections and torque on the long manifold bolts torque is set to 105 inch if iam right (97%) sure of this these matter believe it or not anything on the car any car for this reason has a torque to it some folks will argue but trust when i say torque to specs 1000% of the time
i learned from experience.
if you can also take all of your injector wires off and mark them if needed only to be sure what cyl they came off of and grab a can 6.00 at crappy tire and its called electrical only clearner and give all of them a good spray and make sure this stuff disolves and you might find a huge difference
we need to rule out this before we head down$$ lane
hope this helps
~dave
iam usually around here so if i can i will help as much as i can
take care and happy pacingggggggggggggggggica i also own a 2005 pac 3.5 mind of their own car/truck