Split level home about 20 years old. Water pressure is ok as long as only one fixture is being used, but as soon as any other faucet is opened, the flow drops to a trickle. The pressure and flow does not return until one of the fixtures is turned off. I have replaced the pressure tank with a new 40 gallon unit and have replaced the pressure switch as well. The tank is at 50 psi and the switch is set to 60 psi. New water softener as well. I have had a rural well in the past when we built a two story house and had great water pressure and volume there, no problem with two showers going at the same time and a toilet flush thrown in. That was even with a smaller pressure tank than this one. What is the problem now? The supply lines in this house seem a bit smaller than in the other house, could that alone account for the issue? It's driving me crazy - which admittedly is a short trip...Please help me plumbers!!!!!