A few things id suggest:
Routing your external wastegate in 3 port mode so that the top and bottom of the wastegate are both hooked up to the boost control solenoid. This offers much better control, most of the time. if you PM me I can find a diagram for you. Its usually a little better to run a boost port directly from the turbo. I usually drill and tap an NPT fitting on the outlet of the turbo. You can also do it the same way as the ATP kits and run a fitting in the silicone at the outlet. I try not to run wastegates on manifold pressure as you can have the effect of the throttle closing and manifold vacuum.
As many people have said, check for boost leaks. In a closed loop system a leak can throw everything off.
Try routing a boost source straight to the bottom of the wastegate, just for testing. By eliminating the electronic solenoid, you can make sure everything mechanically is working correctly.
Larger AR exhaust housing. As you have more mass airflow, the pressure in the manifold increases and even the wide open wastegate isnt enough to quell the pressure and slow down the turbo.
adding a cat to the downpipe. More backpressure.
make sure the fire ring is installed on the wastegate (manifold side). However, you would most likely have LESS boost if this wasnt installed as the wastegate will always be venting a little but this is always good to check.
open wastegate test. I have done this a few times on cars with creep issues. Use shop air and a pressure regulator and put 20ish psi to the bottom of the wastegate and do a pull (need a dyno for this). See what kind of boost it hits with the wastegate wide open. This will show if the system has the ability to properly control boost.
Double check your logs and make sure the WGDC is at zero all the time. If the WGDC compensation mode setting is not right (assuming your using cobb) the closed loop system will add WGDC.
Put a lighter spring in the wastegate. With a 3 port EBCS setup you can run alot of boost on a pretty light spring.
MAC 3 port boost control solenoid. I always use these on external wastegate setups. They can flow more and react faster than most stock valves. Boost control wiring is always pretty easy. Theres 2 wires and the polarity doesnt matter.
