I also have a 92 2.3 automatic that shifts very hard. The same car also gets lousy gas mileage (less than 20 MPG around town and barely 23 on the highway). When under warranty, the dealer swore nothing was wrong. The car has always run very hot, poor gas mileage, very hard shifts and seems to "eat" caps and rotors in 20K miles or so.
I've checked for vacuum leaks... nada. Is there any chance that either the fuel and/or ignition modules are bad or could this be a sensor problem??