125 psi unregulated is excessivly high water pressure. If this is true, it should be verifiable by simply contacting your local water district. as a plumber that tests water pressure regularly in several diffferent counties in northern California, I fear the pressure gauge might be faulty. it should always start at zero, if dropped it will damaged and give a false reading. How ever if your plumbers gauge is working correctly, than you need a new regulator IMEDIATLY! Any time a sink faucet (0.78-2.8gpm) is opened and water pressure drops more than 10psi from static psi you need a new regulator pretty soon. if you are getting a 25 or more pressure drop your regulator its bad and needs to changed now. Those kind of pressure fluctuations will break fixtures and many times burst pipes. A tub spout or hose bib will push 4-8 gpm, and will easily drop 15psi from static pressure. with a bad regulator you will see an exponentially bigger drop. Now if your district is giving you 125psi during peak use hrs, it is very likely that you will go through regulators much quicker (ie 5 years) than a district that is pushing 100psi during peak use hours, which can last 7-15 years.

Every neighborhood will have differing pressures. Distance from your local water district, and elevation play major roles in the pressure in your neighborhood. Water pressure will change through out a 24 hr period. Static testing during peak use hours(day) will be different than low use hrs(night). Ask to see if you plumbers gauge. it be at zero when holding it in your hand. it should be metal and glass, without a plastic lens, a gauge with a plastic lens is not to be trusted. if his gauge checks out, have it changed, he if he didn't explain all this to you, he probably is trying to upsell, but got lucky and was right, You need a new pressure regulator . just make sure you are getting an all brass prv from a plumbing shop, npt a box store like the hd or lowes.

hope this helps and Good luck.

Plumber from Nor Cal