Water pressure has slowly been getting worse & worse. Finally just drips. First I checked the shower head even though it is new. There was no problem there. Then I was told to change the valve cartridge. Done. Still doesn't work. Any other ideas on how to troubleshoot this problem? I am thinking of turning on the water partially with the cartridge out to see if the water shoots out of the valve. Then maybe I can at least tell if the problem is between the outside cutoff & the shower, or between the shower valve & the shower head. Is that a good idea? Any other ideas?