If they changed or repaired the pressure regulator, how did they know it worked if you are still having the same pressure issue?
Me thinks you are getting scammed, or they did not put in another "good" regulator. Call em back.
If you bypassed the softener and filtration system, and checked the screens, this seems like the next step. After that it may be time to flush the system.
I once had to change 3 starters on my truck until I recieved a good one, and they were checked out at the parts store...hmmmmm...the last one has been in there 10 years.