from 4th gear, i see my boost gauge rise up to 10 psi perfectly when i put the throttle down, but in 3rd gear it sometimes boosts only until about 5 psi and the needle just hovers around there until i let off the throttle. it still feels like the car is pushing hard though. is it possible for a leaky line to leak pressure in certain gears/speeds while holding steady in others?

 

Here's the boost test:

http://www.fd3s.net/boost_test.html

Do that and report back if you have something working differently than what the link suggests.