The house my fiance is renting has newer well and Gould V60 20 gal. diaphragm tank (less than 5 years old, maybe). The pressure switch was leaking so the homeowner replaced it with a new 40/60 switch. Since then the water runs fine most of the time but occasionally the pressure/flow at the faucets and toilet drops off. The water doesn't stop, just flows very little. The pressure switch is on and the pump continues to run.
The remedy for this so far has been to shut off the pump breaker and turn it back on - the tank fills and faucet pressure is restored.
Thanks to the good info on this forum, I learned to drain the water completely and filled the air in the tank to 38 psi (it was about 5-6 psi low) but the problem just happened again a few days later.

Any help is appreciated - thanks.