Some basic things to check:
Google "AW4 solenoid testing" and follow the testing procedure. You can do this from the connector under the hood or at your TCU with a cheap electric volt/ohm meter.
Test the TPS too. The later years the TPS isn't adjustable, so if it tests bad, you'll need to replace it.
Disconnect your TCU, pull the fuse, any difference...if not it may just be an electrical issue.
If that doesn't turn anything up:
Fluid level, should be checked at operating temp, engine running, in park (or neutral).
Fluid color and smell. If it's dark and smells burnt, that indicates your tranny is working too hard, has overheated or both.
Drain the pan into a container...where you're not mixing it with any other fluid, oil or anything else. Run that fluid through a strainer or screen, a paint strainer is best IMHO and check for chunks of metal, sparkly sparkles etc.
Remove the tranny pan, check for more chunks. Check the magnets at the bottom of the pan too. A little "mud" (like tiny metal fuzz) on the magnets is normal.
If you still can't find anything, take it to a reputable transmission shop to check it out (not to any shop starting with "AAmco". They will surely tell you that you need a new transmission and it'll only cost you $3000+. A good shop will tell you a.) what they think the problem is b.) how much it'll cost for them to fix it and c.) roughly how much parts are for the problem d.) steps YOU can take to fix it yourself. Any tranny shop will charge you $600-$700 to R&R the tranny (remove and replace) before any other work is done. Just keep that in mind when your deciding your course of action.
A couple of things about my torque converter issue. My engine ran perfectly, no issues. I drove the truck (MJ) to work that day and then ran an errand with zero problems. I heard a "whizzz" or a "whirr" going up a small hill back to work. I parked the truck, when I went back to leave for the day it started and ran normally, shifted it in to reverse and ...nothing. Coasted out of my spot, put it in drive...zilch. No bump, no clunk, no whirr or whizz. It just would no go. It shifted smoothly when I moved the shifter...it just wouldn't go anywhere.
So, I'd have to agree with JeepNoob...I kinda doubt it's the torque converter (a re-man AW4 torque converter cost me $220) from a local racing shop that does great work. The previous torque converter I got at NAPA for $145 6-7 years ago. If you decide that you need to pull the tranny anyway, even if you're just changing a front seal. That'll give you an opportunity to check the converter physically.
Checking the converter out of the vehicle involves sticking your finger down into it to the first set of gears/splines. That's the stator. That should turn freely going clockwise and should have resistance counter clockwise until it goes about and inch or two around...and then it should just lock (or be much harder to turn). Good luck.
