i had this problem what it is because u are setting ur boost on the actuater, witch is altering the preload. what u need to do is screw the actuater rod bk, then set the boost by either, bleed vavle, or using the amal valve. I pulled my rod out to make 16psi. but then it was dropping of to 12psi, so karl norris told me what to do,. now it hold 15 all the way. take the rod all the way bk, well not all the. hope this helps if that doesent work, actuater spring may have gone week.