Here are the facts.
1: Unplugging the connector at the rear takes every bit of electrical out of the equation. The Allison will hydraulically default to 3rd, and reverse without being plugged in. So if it wont move with it unplugged something is internally wrong. PERIOD!
2nd: The edge will not read TCM codes. Been there done that. Get a good up to date scan tool. Or better yet get someone with a tech 2 to read the codes for you.
3rd: I would highly recommend you remove the plug in the bottom of the bell-housing, take it to a local hydraulic shop, and get a hose made to go into that hole and connect it to a good quality 0-400 PSI gauge. Then start the truck and report back what the pressure is at idle in park, and in gear.
4th, and most importantly, this trans will have to come out, and be carefully torn apart to be fixed. But you must gather the proper information before tearing it down to determine where the problem is.
Now if you simply want guesses on whats wrong. I would guess that you probably installed the bell-housing gaskets wrong. And that a torrington bearing fell out of place while you had it apart and now its crushed up and going through all your planetaries destroying everything.