I have a 2000, 4runner, 3.4L, 5 speed manual, 4x4, Sport, 4:10, 32" tires, Normally Aspired.
The 3.4L is a good strong engine. It may not be the most powerful. You can either get one with a supercharger or add one. The Colorado altitude takes power away too. Lower altitudes will have more power. Going over the continental divide I have to down shift and sometimes can only go 50-55 mph depending on load. On less mountainous areas I can still go 80mph. Do I wish it had more power? Yes. Can I live with the power it has? Yes.
I did notice a little power loss when I went to 32" tires (I did not regear nor do I plan too. If you plan on 33" tires you will probably want to regear.
My transfer case is the old standard manual mechanical lever "J shift". I can, and do shift in and out on the fly up to 60mph. (little known fact: You can shift out of 4Lo and into 4Hi on the fly too) The multi-mode does give you AWD so wheels can slip (center diff lock) when driving on surfaces that don't require a more locked 4wd. This center diff lock needs to be locked for maximum traction. It can also take a little time to lock/un-lock.
It did not come with a rear locker, I added an ARB. It'll climb some amazing obstacles. I can have the nose up at ~40 degrees and one wheel 3' off the ground and keep going. Personally I believe that the ARB performs better than the e-locker. It'll lock and un-lock instantly (wheels not spinning). I can try an obstacle open and then lock without any roll in. The e-lockers that I have used usually require some roll in distance to lock and then to un-lock.
2001-2002 have traction control. This is the first years for this and it is not a great system. It adjusts engine throttle/power to control traction. This can cause the engine to almost shut down to an idle when it detects loss of traction. This has happened when people are stopped at an intersection and turning left, then they try to accelerate to cross traffic, the engine looses power and you end up crawling thru the intersection. There is a "andy mod" that turns off the traction control by a switch.
There is enough space in the back to build a low profile storage box/sleeping platform that two can sleep.
I have owned mine since new and I now have ~220,000 miles on it. It is running as good as new. I have had no major failures, just normal wear and maintenance.
Gas mileage? I regularly get 18+mpg in combined driving. On highway trips I usually see 20+mpg and have seen over 24mpg.
If I had to replace it what would I replace with? Probably another 3rd gen.