Preemptive sensor replacement and/or preventative maintenance?

So I have a 98 4.0 with about 190k on the clock, and I was just mentally going through the list of what I've replaced and what I haven't. I'd like to hear some opinions on what I should be doing maintenance-wise.

I've stayed on top of, for the most part, the scheduled stuff, but I was wondering mainly about all of the sensors, etc, on the throttle body, intake and all of that. Should I replace them before they go, or just as they go?
What else should I be staying on top of?

Here's what's been done in recent history:
-All the brakes
-All of the cooling system (minus the heater core)
-Steering stuff
-Front hubs, rear wheel bearings
-Diff fluid

Here's what's on my list:
-Tranny fluid and filter.
-Should probably do t-case fluid too.
-Hmm. That's it for now I guess.


Oh, BTW, how many quarts of fluid do I need for a full tranny filter change and for a t-case drain and fill? I know not to use synthetic fluid.

Other than the o2 sensor let them go until there is a problem. If you want to throw a sensor in your "spares" kit a CPS/CKP crank sensor would be a "must have".

Drop the pan on the AW4 and change the filter (or not) and you will need about 3.5 quarts. DON'T overfill, way better a little under the full/max mark than over it.

NP231 2.2 pints; NP242 3.0 pints. NEVER remove the drain plug first. ALWAYS remove the fill plug first. The transfer case fill and drain plugs like to seize in place--if you drain it and can't get the fill plug open, well, the word "screwed" comes to mind.

Good luck.