This same sorta thing just recently happened to my 80 El Camino:
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http://www.chevyasylum.com/80elky/071303_23r4.jpg[/img]
It turned out to be the rear end. As I understand it the bolt that holds the pinion gear to its shaft backed out and snapped off.
I have another rear end on the way (I'm replacing the 2.73 open with a 3.73 posi.)
The way I verified it was to chock the front wheels, jack up the rear end and spin the rear tires with the tranny in neutral. I still had the noise and the resistance. I knew that it was in the rear end then. I'll know more for sure after I swap the new one in and tear the old one down.
Ray
