I have the same question and drive under the same operating conditions as chetJ.
Hoping that 1Engineer would chime in with some general guidelines esp. in cases where auto manufacturers don't off any guidelines a/o there is no reputable info available on other fluids/oils too like the diff and transfer case.
Personally? I would change between 100K and 120K miles.
It is a sealed unit with a very good fluid that is designed to go a long time under normal operating conditions for a vehicle of this type. Now, if you tow 5K 3X/wk or drive in harsh environments like 100's of miles of dirt and mud roads every week. Change it at 60K. If you use it to plow snow (!) or pull stumps as a work truck you might need to change it even earlier than that.
As it stands, very few here would even need to change it (from what I have read) at 60K, much less earlier. Changing it for peace of mind is one thing I guess but I prefer to follow schedules written by someone who knows more about the subject than me.
I tow about once a month on average and take it off road maybe 50 miles a month. My off road is not bad as it is usually mud and dirt and for both work and play.
It's all about the duty cycle guys. If you, for example, run a car top carrier or pull a heavy trailer all the time you are constantly putting the engine and transmission under a heavier load and hence a higher duty cycle. I know the Toyota engineers can't publish a rule of thumb guide because, as I have said before, stupid knows no bounds and is not limited to just Jeep guys, but if they could I would imagine it would be based on efficiency. What is a great measure of efficiency? Everyone talks about it all the time here and it's gas mileage.
Everyone gets different gas mileage to a point but that's just because of different styles and such. Let's say you buy a vehicle that is rated at 20 mpg overall. Let's also assume you get 19 mpg using it normally with no modifications for a month or so. That's close right? Sure it is. Now, let's say you get a trailer and go into the landscaping business or something. You always have it on there and your efficiency drops to say 12-16 mpg. You would be a guy I would recommend to change their fluid on an accelerated schedule. Conversely, if you were a guy who hung 1000 lbs of crap (skids, sliders, bumpers, RTT's, etc) and lifted it and are running 33's, you also would see a huge drop in efficiency from stock. You would also be a guy I would recommend to go on the accelerated fluid change schedule. If you plowed snow with it I would tell you to change it about every two weeks lol because that is the worst thing you can do to a transmission regardless of gas mileage.
My personal rule of thumb for fluid changes is based on efficiency with the understanding of common sense anomaly's like plowing snow. If you get close to rated efficiency of 20 mpg then stick with the long schedule. This means you are not abnormally loading engine/transmission/differentials above what the designers and engineers anticipated. If you do something or have modified it in such a way that your efficiency has dropped 25-50 percent on a continious basis (which means you are loading these components and causing them to work much harder, hence the drop off in efficiency) then you need to change these fluids much sooner. If you go heavy off road and go through rivers or you work it hard like plowing snow then change it even sooner.
Hope this helps.
