when the trans out remove the converter and try and "turn" the imput shaft while installed in the trans.. park it should not turn and as you put it neutral and drive it should turn and possibly watch the imput shaft to turn.. Also if the trans is installed.... with or without fluid see if the truck will roll on its own when its on the flood? i know you said the truck does not move under its own power but is it in a bind??...... What type of transbreak does it have? Do you have to Hit the switch to make it back up?? They have old school trans brakes also there is a Pro tree transbrakes they are different...