Old ford drum brakes

I have a 1977 Ford ranchero. All of a sudden
one morning after warming up engine it felt
like the brakes were dragging really bad. So I
lifed one rear wheel at a time and removed
tire and took the drum cover off. A lot of
black dust present . put car in nurtrql and
turned wheel around a few times back an
forth. Re assembled and repeated procedure
on other side. Care drove fine. But I'm Leary
of any freeway driving. Took the car out
around the block a few times still see fine .
next morning it feels like they are binding a
bit.  What needs to be done? The brakes
look good as the recently done. I've only had
the car about 2 mos. Any advise appreciated
.thanks