Fresh water pumps are positive displacement
and therefore do not need to be primed. They will pump both air and water until you get a clear stream of water without bubbles. You do of course need an air vent going into the tank as water is displaced out of the tank.
If you know for a fact that the outlet side of the pump is reaching its designed shutoff pressure and it is still running then replace the pump. At less than a year old it should still be under warranty.
Pressure reservoirs are excellent in that they reduce the number of cycles that the pump solenoid turns off and on during its lifetime. Sometimes the first thing to die on a pump is the solenoid and quite often that can be from over use. Also, a pressure reservoir reduces the number of times you have to listen to a pump cycling off and on which can get annoying.