[98SableGS]

When is the last time your spark plugs and coil packs were changed. I have a 2002 with a 4.7 L and I just changed all 8 spark plugs and most of them were very loose. Make sure before you take the spark plug out to blow out any junk with an air compressor. Don't want that junk getting in the motor. I would start with the plug and coil pack first, not so expensive and you can do it yourself.

Does your Durango use motor oil?

I have never put any additive in my gas.