OK - solved in my case. This is AFTER I had swapped out the front lever assembly with a new OEM unit (a year or two earlier).
The problem was with the after-market parking brake shoes - the "flange" projected beyond the "web" at the end where they bear on the anchor AND where the web engages the actuator lever. There must be zero play between EACH shoe web and the two relevant mating actuator parts (notches). I found this out by comparing my non-OEM shoe set with a complete OEM backing plate assembly from MOPAR. I now have working parking brakes.
BTW - for the fix I removed the axles, swapped the entire backing plates (loaded), and reinstalled the axles. Sooo much easier than fighting springs and other brake parts behind the axle flanges
