Poor gas milage on highway

I have a 1997 dodge caravan sport 3.0 liter v6. First problem, when I first start it up in the morning, it idles fine until I touch the gas peddle, then starts to stutter like it is going to stall, then all of a sudden revs up. Second, when warm at an idle it does havea random stutter when in gear. Third, I am only averaging about 15-17MPG on the highway, I think that is terrible, or is that about right? I did check one sparkplug today and the electrodes are soso worn. Along with the distrib and cap are also worn, but I cant see changing these items will muchly increase gas consuption, or will it?