I have a 96 ranger, 4.0 v6. I posted a thread my 4wd issues awhile ago and it is still doing it except more often and its getting worse.
I always keep the hubs locked since I live in Alaska and its winter. So when the hubs are locked and it is not engaged in 4wd, there is a grinding sound. I think it is towards the left front of the truck. I am not positive but it seems that it grinds when the truck is going downhill or on a flat stretch.
When the truck is locked in 4wd about every 5 or so seconds, the truck lurches or jumps. And once again its towards the front left part of the truck. It happens more often when it goes more than 20-25 mph.
The preveous thread is here Grinding while in 2wd but not in 4wd.