1970 ‘Cuda AAR Power Steering loses boost at low rpm

I have a '70 AAR with power steering (added during the restoration). At very low r.p.m. (idle), the power steering loses boost momentarily. Not all the time but often enough to be annoying, like when turning into my driveway. Other than that, the P.S. seems to be fine.
The interesting thing is: When I worked for Chrysler during the muscle car era, I had a NEW Dart GTS with a 340, 4-speed and power steering. The same thing would happen. (I tried to compete in a parking lot slalom once and the power steering would lose boost and "lock up" as I lifted off the throttle for the tight turns.)
Is this a known issue with cars of this era or is there something i should be doing to correct the problem?
(FYI, I have also posted this question in another forum.)
Author: AARinOntario