Im looking at buying a new SUV and Ive found a few 98-2001 Monteros that are in my price range with 100 to 130k miles on them. I would like to know what their issues are, in other words what commonly goes wrong or needs taken care of. They seem to be pretty solid machines but Id like some input from people that own and run do more than just your everyday commute. It will e mostly a DD but will see some desert/mountain runs.

Generally speaking the preferred years are 95-96, due to higher HP, locker, stock body height and gearing. In 98 or 99 they went to an un-acceptable diff gearing that must be swapped to avoid stalling and over heating. Of course you could do that, but with a 95-96 you do not. There are some engine update issues to look at that include valve guide seals, intake butterfly, and Main Pully bolt.

I had an 1998 and had no over heating problems. It was wheeled though the desert and rocky mountain trails. I did change the gearing just before I sold it, but saw no difference in performance. The 98 has 10 less HP than the 94/96's, but it's a single overhead can with no butterfly problems like the dual overhead came engines. Most who own a Gen 2.5 model really like them. I would be looking to get a Gen 3 model also. They are coming down in price and I think they would suit your needs just fine.
So before you buy one ask when it was serviced (timing belt, ect.). Plan to spend around $3 to 4 hundred in parts for this service.

What are the stock gears in the later years? 3.73s, 4.10s? Im assuming the overheating is due to the engine working harder because of the taller gears? Im not looking for a real hardcore wheeler for now, just something that will let me do some weekend camping on mountain trails near the Roswell area for a couple months. It wont be heavy wheeling because this will be my only vehicle while Im there and I prefer the better mpg's, at least temporarily. Reliabilty is more important, as I wont have any time or place to fix things. What years are what generations? One more question, you mentioned $3-400 for a timing belt change for parts. What all does this entail that its $400 for parts? I was thinking maybe $50 for the belt, $40-50 for gaskets, maybe $100 for the waterpump(if its under the timing belt cover. Anything else? How hard are these to do at home? Any special issues to the Monteros timing belt change?

It is very interesting. The Monteros are a bit under geared to start with, and they went from 4:60 to 4:22, and it is just enough to make the crawl ratio too high. We even had to turn around stock rigs on a simple Colorado Mountain trail because they were running out of power/ gearing the first time some folks wheeled them. Having the wrong gearing and being under powered is not necessarily best for gas mileage, although I have no question that was the thought. SOHC engines are definitely more reliable. What ever you do look for a version with a stock locker.

Oz never saw 4.2 gears, ours were 4.636 & 4.90 for the turbo diesel. The 4.90 are a straight swap in too!.