First of all those brass reducers fail more than you think. AND yours could also just be plugged up. I only get a few months of use of those cheap brass ones before I have to buy another one. They either plum stop working or get clogged up and reduce the water pressure to a trickle.
I quit buying the brass ones and I am having better luck with the plastic regulator. Go figure.
They make a real nice inline rv regulator that shows the pressure and you can dial it in. Just don't be tempted to put it over what the suggested pressure for RV water lines.
http://www.rvwaterfilterstore.com/PressureRegulators.htm