I went through similar issues with our's, Steve. 96 Explorer rear in the Heap, all new brake stuff. First, I adjusted the shoes just like I used to adjust drum brakes...tighten the shoes until the rotor is locked then back off five or six clicks. But I still had a poor park brake even with the cables tight. I'm using the stock park pull lever but I added a couple of inches to the cable lever under the car. that gave the system a lot more leverage. Still no joy.
Last year I tightened the cables more, and then more, and finally, even more. Now I have a decent park brake with no drag when released. It seems that system just needs to have that lever moved quite a ways before it actually moves the shoes. Crappy system IMO. If I ever get the energy I'll swap to the Mustang rears which use the service pads for park function and work very well, I'm told.