I'd advise changing ALL the fluids. Coolant unless it looks pretty fresh, oil of course, but also the axles, transfer case, brake, and power steering fluid. A full transmission flush on a 168k mile transmission is probably a bad idea unless you know for sure that it's been rebuilt. I would just drop the pan, change the filter, and refill it. For the motor I would use high mileage oil. Max Life, Pennzoil HM, and Castrol HM are all good, as is diesel-spec Rotella 10w-30.
Valvoline Quicky Lubes change the axle lube with a suction pump through the fill hole for about $44 each. At that price it's not worth the bother of doing it myself and taking the diff covers off. I come from the Ranger/Explorer world where that's the only way to do the front diff anyway.
When I drained the transfer case on ours it was about half full of water and looked like Pepto Bismol. I refilled it, they use ATF, and did it again in 5000 miles. The transfer case is not hard to do yourself if you get a suction gun to fill it with.
Some of the Quicky Lubes will do a power steering flush but I just drain the resevoir with a turkey baster and refill it with ATF once in a while.
There is no fuel filter to change, it is part of the fuel pump, but of course check the air filter, plugs, wires, cap, and rotor. When properly maintained the Jeep I6 and 4-bangers will go 200k no problem.
