Things that could cause your problem, assuming your turbo isn't bad:
- boost leak
- exhaust leak
- weak or leaking wastegate
- bad boost controller
How did you not see boost leaks? Did you actually do a boost leak test and listen for leaks and spray couplers and every other mating surface with soapy water?
Replace that cracked gasket with an OEM one. WTF is with making your own gasket? This isn't homemadeturbo.com.
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