If you've got oil in the spark plug tube wells then that's going to be a big area of concern. The oil can soak through the plug wire boot and cause spark to short to the metal tube rather than go through the spark plug and jump the gap.
Next would be the spark plugs. Champion works best for your vehicle and quite honestly, I've not seen a case where autolites worked good any any car for the last 10 years. Many times they will keep the car running for a short period of time but give it a couple of months and they begin to act up. Also, you don't need to fork over the money platinum plugs for this application. The simple copper plus plugs work just fine. Most people think Champion plugs are junk and I do see them as the plug of choice for lawnmowers. But... they really do work wonders in a chrysler product.
You wires would also be suspect now since they've been exposed to the oil. When you do the plugs I'd recomend doing the wires as well just to be on the safe side. Keep in mind if you've got oil in those spark plug tubes then unless you fix that then you will just ruin your new plugs.
I asked about the raw gas smell because the 3.5L had problems with the fuel rail cracking. If you don't smell any fuel then I would not attribute the idle issue to the fuel rail.
The last two things that come to mind are the intake manifold bolts and the EGR valve. The intake plenum is the large piece that sits over both valve covers. It bolts to the intake manifold between the valve covers. The bolts that hold it down to each cylinder head sometimes broke which would cause the engine to pull air in. This can be checked by spraying a carb cleaner in a number of places around where the intake manifold meets the heads. You'll be listening for a sucking noise or a change in the idle (either it flares up or starts to stumble).
The EGR valve is designed to route exhaust gases back in to the intake stream in order to cool down combustion temperatures. Sounds silly but the hot exhaust gases are actually inert and when introduced it really does cool down the temperature a little. Regardless, this device sometimes would stick partially open causing a rough idle or a surge as your at a sustained speed. If you have a vacuum gague then you'd be able to see a slight flutter at idle which could indicate the EGR valve is partially opened when it should be completely closed. If it's stuck open even a little then the computer doesn't know it and does not make the necessary adjustments to calculate the fuel corrections.
I'd recomend starting with Champion plugs, new wires and fixing your oil leaks. j