Forgive me if I have been absent, was dealing with the stresses of a funeral and family.
But just because there is no excessive shaft play does not mean the turbo isn't blown, it could be bad seals, does the exhaust housing of the turbo look clean? Or does it appear to have an oil residue around the center housing? Second, get that boost leak test done, it will show you where you might have any leaks into the intake system. In a turbocharged car any sort of gasket leak/boost leak can mean a loss of power. If the boost leak comes back with positive results, the next thing I would do is a Cylinder Leak Down test, which is slightly different than a compression test, but if your uncle is a mechanic, he will know exactly what a leak down test is.
After that, the only other way we can continue to help you is by providing us with some datalogs to look at, other than that we are just phishing around in the dark for answers without knowing the whole picture, and a datalog would provide exactly that.