Rear wheels seem locked. They turn the same speed and tires bind/grind turning.

Limited slip additive. Is that what it's called? Just add to rear differential? Thanks much pushrod, keep pushing.

Yep

Would like to know from Larry if this fix it worked..... I have exact same problem with my 2003 mountaineer.... I have has three mechanics look at it and they are all puzzled.... Please email me bcatron@hsc.edu