Ok Guys, Im a 4G guy but this is a pretty general question. :P

Ive been having troubles keeping my boost pressure up.
Say I set my Joe P. Manual boost controller to 25 psi.
When I do a pull itll raise to 25 psi, then fall to 19psi.
The internal wastegate is set to 18 or 19 psi.
No matter how high I set the MBC it falls,


If I put the boost source right on the internal gate actuator itll boost to 18psi and stay there all the way to redline.

Is the spring in the mbc getting weak? (its 3 years old)
Ive done a boost leak test, none found.

I pulled the hose off the actuator and made sure the wastegate wasnt blowing open. It held all the way to like 29psi where I let off.
I also feathered the gas as I was driving to make sure it would hold 25psi for a little while

Any ideas?

Your probably right about the boost controller getting weak.

Pretty much the obvious answer considering your good diagnosis. :P