At 70 MPH on the highway my 91 Accord LX Automatic tach's at approximately 3000 RPM's in 4th gear. If I accelerate lightly from that speed I notice that the RPM's will drop by a few hundered RPM's as the car begins to gain speed. If I lighten up slightly on the gas pedal the RPM's will go back up by the same few hundred RPM's. The change is abrupt and repeatable and does not feel like it is slipping.

I have only owned this car for a few months but I have never experienced this before with any other automatic tranismision. Is this normal? What is the cause/reason?