I had an 89 Pathfinder, freakin bulletproof but it was a manual. I would be leaning toward the torque converter as a plausible solution, the tranny seems confused and unless you were towing something they dont just shit the bed without a little heads up. You got fire, air and fuel which leaves you with logic (early computer stuff in the late 80's). Transfer case sounds okay since it wasn't relevant prior to your problem. Check your connections and even a fuse could be your problem.. Somewhere's along the 10/15 amp regime. After that, I would break out the manual, order/pull the part and you should be 5.0
+1 follow this advice
it's always such a great feeling to find that all your electrical woes are the result of a fuse
not saying that it is in your case, but you wont know until you check.