You mention a pressure regulator. If it is one of those Walmart types, it could be the problem. The outlet orifice in those regulators is very small. and restricts the flow (volume of water( passing through. To test this, remove the regulator and see if your flow increases. If so, get a Watts whole house regulator. and install it. Your flow problems will go away and you will still have regulated water pressure.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))
2003 Fleetwood Expedition 38N 2005 Saturn Vue