Had new transfer case put in a 2000 Bravada mechanic says motor keeps running on 2000 Oldsmobile Bravada

So he now has to put in another one its for a 2000 Bravada all wheel drive with smart track

Asked by for the 2000 Oldsmobile Bravada
your question is
What would still make the motor keep running n break another new transfer case they can't figure it out so I'm stuck waiting on them n I need my Vehical.