I have slowly noticed low water pressure, whole house. Copper piping. Regulator replaced 9 years ago, it is adjustable.

If the problem is not in the regulator it could be your service line. I live in Texas and we have alley ways for the city services to be installed in and we have to run a service line from the house to the meter which is in the alley. So I am thinking that even though you said you pipes are copper some of the service lines are a galvanized iron pipe that is very bad about corroding and filling with rust.