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?