1) Check the ECU for codes. Boost is controlled by the computer, if something it doesn't like is going on, it'll pull boost.
2) Hoses are fine if you're getting too little boost. If you blow a line off you'll get too much as the wastegate(s) won't open. Check the boost control solenoid, though.
3) If you're running cats, check to see they aren't toast/melted/etc. Blocked exhaust will cause a major reduction in boost.
4) Check for any leaks on the charge pipes between the turbos and manifold. The stock hoses are fairly crappy. Be sure and remove the heat jackets and check the hoses at the turbo side as well as all the clamps.
If you have no ECU codes, the control valve checks out, no boost leaks, and the exhaust is fine, it's time to start looking at the wastegate capsules and turbos.