If the voltage from the DAC is stable, the reading should be stable from the APM too.
Where are you seeing these readouts? If you use MissionPlanner, you’ll see “rxrssi” under the “Status”-tab below the HUD on the flight data screen.
If it’s on the MinimOSD, it could be a number of things. (That is best not further discussed in this thread, as it has nothing to do with APM:Plane 3.0.0)
I did as you suggested and checked the rxrssi value under the Status tab. Like the MinimOSD it was erratic. I then checked the voltage on the RSSi pins on the RCRX. Erratic. BINGO! I changed receivers and problem was solved. Really appreciate the help.