I hope this helps but if not there is a wealth of other websites that are helpful such as carsurvey.org, planetisuzoo.com, independent4x.com (aftermarket), wikipedia and consumerguide.
1984 - Isuzu introduces Trooper into U.S. 1.9l engine. 4 speed transmission. Automatic locking hubs. 10 gallon gas tank (identified by the gas filler in front of the rear axle). Round sealed beam headlights. Antennae on drivers side windshield pillar. Two doors. Rear seat has horizontal sliding windows. 15x6 rims with P225/75/15 tires
1985 - Won the 4x4 of the year from Petersons 4wheel drive magazine.
1986 - Isuzu Introduces Trooper II into U.S. (This was the same as a Trooper, but with no rear seat at the time of import, so it was imported at a lower tariff rate as a truck. Rear seat installed by dealer). 2.3l carbeurated engine, or a 2.2L turbo diesel bolth had a 5 speed MSG-5 transmission only made for 86-87 troopers and pup 4x4s. 10-bolt (Isuzu Corporate) rear differential. 8-bolt (Isuzu Corporate) front differential. Tachometer added to gauge cluster. New gauge cluster added between center vents with oil pressure, temperature and gas gauge. 4 door model offered. Two door model has same body as previous years. Rear spoiler (used to keep continuous air flow across rear doors to help prevent exhaust gases from entering) and roof rack offered as options. Air conditioning a non-Isuzu dealer option. 21.5 gallon fuel tank located behind the rear axle. Alloy wheels on LS model.
1987 - Transition begins. Square headlights like later models. Same driveline as 86. Some report 12-bolt rear end and 10-bolt front end differential, though officially the 10/12 combination was not released until the 1988 model year. also last year for 2.2L T\D engine. first year for LT235/75/15 tires.
1988 - 2.6L 4ZE1 (121hp / 146 lb-ft) fuel injected engine introduced. MUA-5 5 speed manual transmission standard with Aisin-Warner A340H 4 speed automatic as an option on the 2.6L. 12-bolt Isuzu rear differential introduced. The 10-bolt rear diff used in rear of '84-'87 Troopers moved to the front in the improved IFS. Antenna located on front passenger's fender. Rear step bumper on LS and higher models with tow package. A "Special Edition" Trooper featuring special badging and a split rear seat that converts to a bed was available this model year only. (Note: the split rear seat that reclines all the way down to the cargo area behind the seat was available in later years as well).
1989 - Short wheelbase RS version with 4ZE1 2.6L is produced and available in the US only in this year. On long wheelbase models, the GM 2.8L V6 (LL2) is introduced as an option as well as the 4 speed GM 4L30E automatic transmission, available on the 2.8L V6 only as the 4ZE1 2.6L was paired with the A340H - an Aisin transmission. All 4L30E and MUA-5 manuals had gear driven transfer cases, while the A340H had a chain driven transfer case.
(Taken from
http://wiki.planetisuzoo.com/index.php/Troopers)
1993 Isuzu Trooper: A 2-door RS wagon joined for 1993 on a wheelbase 17 inches shorter and measuring a foot shorter overall. Trim and equipment for the RS were similar to that of the 4-door LS.
1994 Isuzu Trooper: Four-wheel antilock braking became available on S and RS models this year, and standard on the top-of-the-line LS. Rear-wheel ABS remained standard on the lower-priced models.
1995 Isuzu Trooper: Trooper added dual airbags for 1995, as the 2-door wagon disappeared. All models now had four doors and Isuzu's unique 70/30 split rear doors. The new instrument panel featured stalk controls for headlights and wipers.
1996 Isuzu Trooper: For 1996, Troopers finally got a new 4WD system for shifting in and out of 4WD High while on the move. All models now had a single-cam V6 engine, but rated at 190 horsepower instead of 175.
1997 Isuzu Trooper: Four-wheel antilock braking was standard on all Troopers for '97.
1998 Isuzu Trooper: Isuzu made two important changes to the Trooper for 1998. First, they added a bigger and more-powerful V6 engine. Displacing 3.5 liters, the new V6 made 25 more horsepower and 42 more pound-feet of torque than last year's 3.2-liter. Second, they made standard a new full-time 4WD system. Called Torque-On-Demand, the system normally operated in rear-wheel drive, but automatically sent power to the front wheels when wheel slip was detected.
1999 Isuzu Trooper: Changes were few this year. A first-aid kit became standard and the Performance Package added fog lamps and available gold trim. This would be the last year for Acura's Trooper-clone, the SLX.
2000 Isuzu Trooper: Rear-wheel-drive models became available, as part of an expanded lineup. Previously, Troopers had been 4WD only. S, LS, and Limited models replaced the lone S model of '99. Troopers gained a new grille and taillights, and automatic climate control became standard. Automatic transmissions were revised in an attempt to minimize gear changes on inclines. Isuzu stretched its powertrain warranty to 10 years/120,000 miles.
2001 Isuzu Trooper: An Anniversary Edition was added in celebration of Isuzu's 85th year.
2002 Isuzu Trooper: Trooper closed out its run unchanged, to be replaced for 2003 by the Chevrolet TrailBlazer-based Ascender.
(Taken from
http://consumerguideauto.howstuffworks.com/1992-to-2002-isuzu-trooper-7.htm)
I also can say that the 98+ models have longer control arms for better flex. And in 2002 they revised a gas line that, in safety tests was found to be faulty and could result in a fuel leak in the event of a crash. They also revamped the 3.5 so it wouldn't burn so much oil. I personally dont have any first hand experience with the Trooper as I am forced to do my expeditioning in a suh-weet Expo white 1994 Oldsmobile 88 until I finish school (can't wait). I will also go on to add that one of my main draws other than off roadability is the studio apartment that resides behind the front seats. The cargo area on these pigs is cavernous and is able to house a sleep platform in addition to a mother in law suite, which is perfect because I dont want to pay for hotels when I travel and I am lazy, I love to just hop in bed when I'm tired. I hoped this has helped and if you have any more questions feel free to ask me, or any of the ridiculously helpful members on this board.