Do not rule out a OVER HEATED turbo assembly. That can start the early begining of a preignition due to over heating. Or hot spots on the turbo. Non standard turbo is always fun if no local help is available.

Try to find some I D on the turbo housing & go to the company for help. Revving up a turbo in neutral is not much help. No real loading on the engine or turbo. Pretty much need a car dynomometer to get useful readings. Not a cheap thing to do.

Timing is a easy check . The other possibility is you ECM can not control the fuel mixture correctly........... A car dyno is the best test. A exhaust gas temperature would also help. A good dyno shop always does all the tests the first time to get real numbers.