I found the RV water pressure regulators sold at camping stores go bad, often. From being gummed up with iron from CG well water, etc. I too spent some time trying to track down water problems only to find out buying a new pressure regulator fixed the problem.
The plastic ones don't last as long as the brass ones. But that said I have had 2 of the brass ones******out this past year. They don't make them like they used to.
I found the Valterra brass regulators with plastic screw on lasts longer than the Camco reluator does.
And if you buy this one with the meter at least you can see and know WHEN they are broke! :C

I full time so my regulators do get a work out and have to deal with ALL types of nasty CG well water!