Using Alt-D Versus Shift-D I'm aware of the difference between Alt-D and Shift-D; however, when I attempt to move objects modeled as rigid body that I've duplicated with Alt-D, they snap back to their original location.  

When I relocate these same objects, duplicated with Shift-D, this doesn't happen?  However, I then have to go into the Rigid Body and change data on each one separately.

I'm using 2.8, new to me, and I apparently don't know how to make sure I don't have Snapping on somewhere...or I'm not doing something else right!  In any event, would certainly appreciate any help!
After you duplicate and place your object, try invalidating the rigid body cache.

One way to do that is by entering and exiting edit mode and jumping to the start frame (ShiftLeft). You'll notice the colored bar along the bar along the bottom of the timeline changes color, which indicates the cache is no longer valid.