all that stuff plus clean out your intercooler, check timing(both valve and ignition), check boost level, fuel filter, check fuel pressure, clean out air filter.
Also, check the gasket between the turbo and the exhaust manifold. I saw a post on that once, the guy had so big a leak there that all the exhaust pressure leaked out there and didn't get into the turbo.
Also if you have no leaks but no boost either, check to see if your wastegate actuator rod has fallen off. Mine did and I had like 1 psi. Felt like a tuned Honda
Check your exhaust for big bends, kinks and or blocked off pieces, or a plugged cat.
if all that fails, take out the 2 dead bodies in your trunk.