My automatic 2001 Corolla LE just hit 60,000 miles. I've been getting poor gas mileage, an average of about 23 MPG for the last few tanks. The engine has been sounding a little rough and it's been shifting pretty hard. I do not think this car should be having these problems this early in its life. There are no check engine lights on or anything and I have no idea what's wrong with it. I'm going to rotate the tires and change the oil and oil filter, the air filter, the spark plugs, engine coolant, and possibly try to change the transmission fluid in the hope that this will solve some of my problems. I've only had the car since about 47,000 miles and have no idea if the spark plugs or the transmission fluid have ever been changed. Some of that is stuff that the scheduled maintenance guide that came with the car says to do at 60,000 miles, and some of it's not. I need to know whether or not I should attempt to change the transmission fluid myself, and if so how to go about doing that. I also need to know how often most people change the spark plugs in their Corollas, what kind of spark plugs to buy and what to gap them to. Also, if any one else has any other suggestions as to what to do about these problems, that'd be great.