I likely called the diff the wrong name. It is in fact, a TrueTrac.

I'm elbow deep in upgrading and rebuilding the front end of my pick-up, but will check out everything using the tips suggested above.

Thank you to all those who offered suggestions and techniques to figure out what is going on. I very much appreciate your knowledge and time to post. I'll post the outcomes of the inspections as soon as I can get to it.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)