Question
I have recently primed my pump, and when I start running through the zones they start off well then the pressure declines.  I have just recently replaced the pressure valve and other connections since they were taking in air.  The water pressure has not changed it starts good and then with a minute or two the pressure goes down.  The pressure gage for the pump reads between 10-15 psi and will not go above that until the system is shut off.

Answer
You may have a problem with the foot valve of your well line, or you may be having water table problems.  The foot valve is at the bottom of the well pipe, and helps keep the line primed when the pump is off.  If the problem is not that, I would suspect that the water table in your well has gone down, and you may need to lengthen the well pipe so that it is below the water table.