ok, i've been a bad jeep owner... 8 months ago my jeep (2004 liberty, 4wd, 60,000 miles) had a major tune up, oil changed, tires checked- all that good head to toe stuff. right after that, i moved to florida (from maryland) and have not had an oil change since. (i've been broke, and keep putting it off- and yes i know, its gonna cost more in the end but when you're living hand to mouth, its hard) anyway, its so HOT here, so i have the AC on almost all the time. i used to get about 275 miles out of a tank of gas, but the past few months i barely get 180... and now, my transmission (automatic) with do these crazy things sometimes where it will rev when i stop, or drop so low once i stop i think the engine is about to die, etc.. the engine light comes on, but then other times it will go back off on its own. what is happening? will a simple oil change fix this, or have i really screwed my poor jeep? PLEASE HELP!!