95-97 engines have the newer OBDII diagnostic system compared to the earlier OBDI version, this really means little to you and me as the reliability is the same. The OBDII system uses a Mass airflow sensor instead of the earlier more restrictive Air Flow meter, along with a few other sensors added for a more advanced and efficient diagnostic system. I think these engines get slightly better fuel economy and throttle response than the earlier models but not much. Otherwise its the same 4.5L engine.
The transmission however is a different unit, some say the newer 95-97 A343 transmission has a more car like smooth shift between the gears but are not quite as stout overall as the earlier A442 model. (will probably get burned for saying that!)
Obviously the interior had a few changes also like the dash and control layout.
I drive a 94 and I love it, but if I had to do it all over again I would probably get a 95-97 truck but I am certainly not disappointed with mine.
plenty of info on here...just need to search for it......