matt is right (mopar) champion copper plugs ONLY every 30k miles.i have worked on dozens of newer jeeps and there really picky when it comes to plugs weather there worn out or a diffrent brand (like bosch platinum 2's they really don't like those),and atf+4 in the trans every 30k miles also.engine oil brand shouldn't matter as long as your using the right viscosity changing when you should and not using wallmart supertech oil lol. clean the throttle body also, old rag/tooth brush and small amount of carb cleaner it WILL make a diffrence.i have done all that and with 265/70/17's and a 3.7 still get 21mpg highway, 15 to 17 city.