Cherockee

I'm posting this for a friend hoping we can lend him a hand and help him out.

The vehicle is a '98 5.9L ZJ. Has roughly 100K miles on it and until last week was driving well.
Symptoms: Vehicle loses power to the wheels and noise appears to be coming from the transmission. Moving shifter between reverse, nutrel, drive, 2, 1 the noise may change or go away completely. Jeep might move a little bit or do nothing at all. Then sometimes it will engage and allow the vehicle to be driven around the parkig lot. Sometimes when shutting off the engine will allow the trans to engage when restarted but the problem will quickly show itself again.

First time this happened the Jeep was left to sit for a couple hours while waiting for a tow truck. When the roll-back arived the Jeep could be driven on the the truck without a problem. Once the Transmisson Specialist got the vehicle he drove it around without any problems or any noises. Changed fluids/filter but did not notice anything unusual (like burnt fluid, metal shavings, etc). Test drove the ZJ and all appeard to be normal.

Having the Jeep back for a couple days and had no issues with it at all, then suddenly it started again. No power to the wheels. Didn't matter if I was in 4hi or 4lo. All the same issues as before. Have not been able to get the Jeep moving very far so we're leaving it sit for the night. May try tomorrow to get it moving at least to get it to the trans guy without towing this time.

I can not confirm where the noises are coming from but I suspect either the viscious coupler in the t-case or the toqure converter (I'm betting the later as that's where I think the noise is loudest-kinda hard to tell).
I'm still searching the forums but have had no luck so far. Has anyone had a simular problem as I have described? Can you offer any feedback. Your help is greatly appreciated. Thanks!