stick in reverse,if it goes backwards box has died,
juck up 1 wheel & if you can turn it freely something inside the Tbox has died,
start it up & have some 1 put it in drive & see if any of the props turn,due to it being a borgwarner & it not driving i dout its a diff etc,
IMHO it might be the tail shaft coming out the box cos the way an auto works there aint anything that can really go bang & cause a loss of drive,then again in ther Tbox its either the input shaft or the chain