I saw this when I didn't have time to write a reply, then it got pushed down far enough to loose track of...
Anyway,
The power thing, I had a flaky one, never got to troubleshooting it, the car got too rusted to bother. I ended up getting my 93 before I spent the time on the belt system. I have a set of the regular shoulder belts I intend to swap into my 93 that currently has the automatic belt, when they start to act up. I HATE those power belts.
The lap belt, should pull out at normal speeds. If you pull it very quickly, it should lock. It's just a mechanical thing, RPM throws weights out [kind of like a governor] and engage a catch.