I'll go along with All58Parks, either there is a valve or a plugged line somewhere. I'd start by disconnecting the output line from the pump and run the pump. If the problem continues, remove the pump and disassemble the pressure switch section. If you don't find a blockage after removing the switch, replace the pressure switch assembly. They are available on line I'm sure or from an RV or Marine Store.
If the problem disappears after removing the output line, then close the valve from the tank to the pump and from the pump to the system and pressurize the system with your water hose attached to the city water inlet and check all the fixtures.
I know that visually following the lines is hard but we all have that problem, you just need to be persistent and try. Almost all systems have a series of valves to shut off the water or by pass the WH and or the pump and isolate the fixtures. I wish I was at home where my system drawings are that show typical configurations, not locations(no one can show all of those)but configurations. Sometimes that helps make the job easier just knowing how things are configured.
The system is very simple it's the confined spaces we have to work in that makes things difficult. Good luck and let us know what you find.
"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson
David Bishop
2002 Winnebago Adventurer 32V
2009 GMC Canyon
Roadmaster 5000
BrakeBuddy Classic II
