I realize this may not be the easiest solution, but from the sound of things there is no nipple on where you connect the vacuum line to? It sounds like you just drilled a hole and shoved the line in.
I would take the pipe off...and have someplace weld a nipple on there for you. then you can clamp it down and make sure that no air is escaping, which would prevent the wastegate actuator from getting a good signal and not opening.