A bit more info would be helpful. What is your water source, municipal, well, cistern for example? Where do you read 100 psi? I have never heard of water pressures for residential this high, ever. Please explain what and where is this "pressure valve" you have changed 3 times.

I have 120 psi into my house and then it goes to a pressure regulator to drop it down to 60 psi, which is plenty.

the water source is municipal. the pressure is over 100 psi is before the regulator valve which drops it down to 50-55 psi. the regulator has been changed 3 times. i cannot find out why the pressure drops after a minute or two after turning on a faucet/shower. thanks for the responses so far.

Pressure reducing valve. When you replaced it, did you get one with the same rated flow? Can I safely assume that this is a PRV inside your house and not outside on or near the meter?

If it's anything like the Watts I have, you can adjust the pressure via the screw on the top upwards a bit. Say like 60psi.

I think you are on right track

Sounds like an undersized PRV.