Question
I have one valve that works great on manual.  But when I have it run from the controller it has very low pressure delivered to the sprinklers.  I have replaced the solenoid and the diaphragm with no change in performance.

Answer
For some reason the valve is not opening fully.  Try adjusting it by opening it all the way, then close it all the way, counting the turns.  Then open it back halfway.  If this doesnt work, you may have a clogged port in the valve that is not allowing it to open.  This means removing the top part of the valve and cleaning out all of the ports (holes) in it.