The 3.5 is the oil burning engine. The problem stems from the oil returns in the pistons being too small and clogging up with sludge. They supposedly fixed the problem in the later 3.5s, but I am not sure. I know my wife's 2000 drinks oil. We have to ad half a quart every three days. The 4l30e automatic is a pain in the ass to maintain. No dip stick, so to check the level of fluid requires getting under it while its running. I use two sets of ramps to accomplish this. Also, like with any automatic, heat is the killer of these transmissions. Luckily when we bought my wife's it had just had a re-manufactured transmission installed with a heavy duty transmission cooler installed. Another issue that can drive you nuts with these things is the TOD system found in 1998-2002 models with the automatic. When it works, it works awesome, and frankly, it works most of the time. The only problem is when it does have a malfunction, the troubleshooting is a bit of a pain. If you decide to get a Trooper, or any Isuzu for that matter, you should join the forums at planetisuzoo.com. Lots of good information over there. Even with the problems I just mentioned, I still love the wife's 2000 Trooper as well as the 1989 Trooper I have as a daily driver.