Check the screens on the ends of the faucets and in the shower heads. We were having a similar problem with presser continuing to drop, and I found "grains" of calcium in all of the screens. Cleaned them out and pressure was restored.
Rick and Janice Binns
2006 MS 32TK3, Mor/Ryde Pin Box and I.S., Auto Level-Up
2012 Ford F450 6.7 L Diesel, air bags and 25K Reese Signature hitch (factory installed)