OK, so I'm posting this for my father, so I may not have all the pertinent info right away, but here's the problem: To my knowledge it's the 42RE trans, not great from what I've heard. He bought the Jeep out in Wyoming, frequently drove it around, seemed perfectly fine. He made the 1700 mile trip back to Michigan (nonstop) without a problem. It drove fine for a few days after, then he mentioned it was starting to slip a bit. A few days later it completely gave out, had it towed back home. Reverse still works. He says the fluid is not burnt.

So, given that the fluid isn't burnt, is there something else that might've failed internally over a 1700 mile straight drive?

Anyways, can an AW4 be hooked up? Would it be a lot of work? Should we stick with the 42RE and replace or rebuild it?

 

Swapping in an AW4 is very time consuming and would end up costing more in the long run. Have a transmission shop check it out, it could be something simple like a bad shift solenoid. There is no shame in having a pro look at it, it might even save you some coin.

 

There's no shame in have a mechanic look at anything, despite what everyone seems to think here.

But then again most people on this forum still live with their mom

 

Usually it's the forward clutch drum that wears out. This is stressed by shifting into drive while still rolling in reverse. My 97 ZJ tranny was rebuilt and the guy who did it told me it's a common fault with this one. He showed mine to me and it was whipped! He put a "good used" one in on the rebuild. According to him, DD jeeps are usually okay, but ones used off road tend to wear out faster. Well, Yeah!

Mine had deep grooves where the driven plates had worn into the slots.

 

Well, if they're like the solenoids on the AW4 I can just test them myself. I suppose we'll end up tearing into it and seeing what's wrong, but I'm out of the country right now and my father is busy with work. Figured I'd get some advice in the mean time.
Good to know, I'll have to look into that.

 

This is true but absolutely not what will give driveability issues. The drum gets worn from the band. If the lining of the band is worn off the rivets will eat the drum, much like a metal to metal brake pad.
The tabs do get worn, and they wear the notches of the sun gear, but as long as they are intact it will operate. In fact, almost everyone I have ever looked at was like this. (not just one or two)
Does it move in any other gear, like manual low, or second gear? manual low applies the rear band and may get it to move, let us know if thats the case.
Otherwise it would be my guess that the direct clutches are gone. They are applied in reverse, but they will still usually back up with the rear band and full line pressure in reverse.