It currently seems to be stuck in 4H

Thanks for the reply and I don't mind you asking at all - totally logical question! Unfortunately as far as the warranty goes it's a little messy in this case - the vehicle was a test vehicle (my work does vehicle bench marking and auctions them off at the end of projects) and some of the ECU wires were extended for recording signals. All the wires are still connected but I know if I take it in for warranty work before I get the chance to remove the extensions and resolder the harness wires that they'll most likely turn it down for these modifications, even though the transmission wires weren't fiddled with (I know there's still a chance an ECU wire could cause an issue with communicating with the transmission, but I figured I'll get the harness repaired first).

On a different note though - I was able to get it lifted at work and with all four wheels in the air, I found out it is not stuck in 4WD. It was still binding however, so I believe it could be something related to the rear e-locking differential instead (all fuses are fine though, and the vehicle seems to think it is unlocked as far as dash indicators go). Do you know of any things that would be good to take a look at with these symptoms or is getting a better scan tool still the best recommendation?

And just out of curiosity, with your professional experience do you have any recommendations for more advanced but still reasonably priced scan tools? I work on vehicles enough on the electronic side on my own time that I wouldn't mind spending maybe $150.00 to $250.00 or so on a decent one, but only if it could read at least most of the various modules on newer vehicle (not just the ECU and TCU like most basic ones do). Mostly Toyota/Lexus, Ford, GM, and maybe Honda. I have looked into some on my own but always would rather get a good opinion from a professional.

Sorry for the very long reply. I hope I'm not wasting your time as I know it's a little bit of a different situation but thanks anyway for your help!

Oh okay got it. That makes more sense regarding the coil and whether the TCCM would be able to tell what state it is in. I hadn't seen this reply yet so I haven't yet been able to try disconnecting the C1591 connector, but I did have it on the lift earlier and switched the locker knob between on/off a few times but it was still binding very noticeably when I first took it off the lift and tried to turn the truck. However, I repeated this one more time (just hoping for some luck I guess) and the wheels were turning in opposite directions when I moved one by hand. I put it back down and didn't feel any binding at all as I turned out of the workshop, then felt it binding again for the turn out of the parking lot, but then it seemed to disengage again after just that one turn (I didn't touch the knob or anything). It was fine going to the gas station and then back. As this seems to be intermittent I will try giving it a short drive after work again tomorrow and if/when it starts binding again I'll try and get it on the hoist and disconnect that C1591 coil connector.

By the way, in answer to your questions, the truck does not seem to respond in any way when pressing the rear axle lock knob in/out on the dash, though I will try putting it into the locked mode and turning the wheel by hand and then turning it off and trying this again to verify. For the 4WD portion of the switch, if I turn it from 2H -> 4H, a dash indicator appears saying it is switching to 4H and I can hear the vacuum actuator running for a few seconds until it finishes engaging and the message disappears. Very similar for turning it into 4L, though it first prompts me to put the vehicle in Neutral. When I go back to 2H from either of these, it gives a similar message saying it is transitioning to 2H (though from 4H -> 2H I don't hear the vacuum actuator running for a few seconds as it did in the other direction).

I will try and see what disconnecting the coil does once the lifts are free after work tomorrow. Thank you again!