[wingnut60]

oldbird,
If pressure is ok with the pump, but less with utility source, then the restriction is somewhere between the entry connection and where it ties into the rest of the system.
Should be a check valve just behind the fresh water connection in the service bay--you access the area thru the basement doors past the water heater. Its hard to reach, but doable--had to replace the check valve on mine couple of years ago--don't get a replacement until you get the old one out, as there are a lot of variations available.
You can also just disconnect the water line into the filter and aim it outside then have someone turn on the water supply--this should give you a clue if the restriction is somewhere before the filter.
Joe