Fuel Pressure with mech. pump ?

I have been flying my RV-8 IO-360 for over a year now 115 hrs , the eng has 325 TTSO and I installed a O/H fuel pump at the O/H . The mech fuel pump has always pumped in the 22 to 24 lbs. area in cruse power . I noticed last week it has dropped to 18.5 to 21 lbs. in cruse . BTW the Air Flow elect boost pump pushes it up to 33 lbs then settles at 26 lbs in cruse . I have opened ALL the screenes and checked them , ALL clean . No leaks in my system . I blead the hose to the fuel sending unit . and also checked the pressure readings with a borrowed mech. gage and long hose . same pressure readings . So my sensor is right on . I understand that my Operating Pressures are from 14 psi to 45 psi , in the GREEN ! So you might ask me , WHATS MY PROBLEM ????
Well the pressured dropped a little from NORMAL ! Is this a SIGN of something wearing out in the Mech Pump ? Like a SPRING ??? Will it wear slowly ??? I don't know if anyone has an answer for me but I would like any in put you can give .
Also the Mech. Pump p/n LW-15473 advertised 24/ 25 lbs. pressure new .

FYI / Mech. Fuel Pump Pressure

I called Aero Accessories and talked to the Tech. about my O/H 'ed High Pressure Fuel Pump. He told me to check for O - ring air leaks at the fitting , it could be sucking air , which will lower the pump pressure , he also said to check all screens , lines and so on . which I did . He could not say if my pumps lower pressure was the fault of my pump , but offer to check it for me if I sent it in to him , for no charge . The last thing he said to me was ,
NO High Pressure Pump O/H'ed at Aero Accessories is sent out unless it is putting out 25 to 30 psi pressure . That being said I ordered a "NEW " not O/H'ed (LW15473 High Pressure Pump) from A.C. Spruce last night to replace my pump which is still putting out 19 to 20.5 lbs at cruse power .