My wife was out of town driving the tahoe when as she explains a big 'cling/banging' noise. she smelled rubber as the truck stopped almost immediately. I can hear and slightly feel the transmission working, but it wont move the truck at all. I figure it's either the REAR END or a locked REAR BRAKE, but I don't know how to tell which one it is. Can someone please chime in and help me troubleshoot this thing? I would greatly appreciate it.