A few things I’ve learned over time that contribute to this issue are,
1 The temperature of the air out side
2 How hot the actuator is.
In cooler weather I have seen more boost pressure ~1-2 psi with no changes.
And at the track I have seen my boost drop off a psi or two if I do back to back run.
This was with a stock actuator with my HD actuator and Holman (ball and spring) boost controller I rarely see a 1 psi change at any time, but opening my dump will gain me boost and faster spool up.
I’m not saying you will have the same results as me but I would take note on the two things I mentioned. These cars do strange things some times. Good luck with getting it sorted out.
P.S. my jam nut is always loose; lock tight didn’t work for me on it.