there is a way to force the TCU to give up codes, just like the CEL.... man, I wish I remembered how to do it. I think it involves pulling out the transfer case shift boot and messing with one of the harness connectors under there... Anyone else remember?

Things to check:

1. your fluid... is it low? is it *any* color other than pink? Brown fluid means your shizz is burning, check for other problems, check for plugged or kinked cooler & lines, fluid leaks, etc. DO NOT OVERFILL THE 4L30E IN OLD TROOPERS!!!!! IT WILL BURP OUT THE FILL TUBE ONTO THE HOT EXHAUST MANIFOLD AND BURN YOUR RIDE TO THE GROUND yes, really. there was even a recall about that.

2. your temperature - is the trans getting way hot? do you feel heat radiating at your legs from the "hump" in your floor? are any of the wires that hug the transmission (look under the truck) melted? (yes, this can happen)

3. your shift lever position - does the little orange flag line up with the gear you're in exactly? do you have a body lift?

4. your fuses... check all the fuses under the hood, in particular the one for your reverse-lights AND the reverse lights themselves (yes, burned out reverse-lights or their fuse WILL throw a trans code)

5. wiring harnesses - check the ones on the passenger side for ugliness or corrosion. If you want to be thorough, unplug, clean, and apply electrical grease to all of the plugs there in that big wiring cluster behind the battery.