Duramax engines have always come with solid turbos. However after miles and miles of whistling and boosting, your turbo may have problems. Or you may have other issues, that make you think your turbo has problems. This is very common as most drivers watch boost, keeping an eye on how much PSI they're making. It stands to reason that if your peak boost drops, your turbo has a problem. This is usually not the case though. More often then not, when we diagnose this symptom we find there are other problems leading to a lower than expected boost number.
Target boost numbers for the following RPO's are as follows (PSI)
2001-2004 LB7- Stock 20-22, tuned 24-26, tuned with PPE boost valve 28-31. Failure will occur near 34psi
2004.5-2016 Stock 22-24, Mild tune 27-28, Hot tune 33-35
The factory map sensor which electronically measures boost on a 2001-2004.5 trucks only reads to 22-24 psi, 2006-2016 MAP sensors read to 37 psi. If you want to read boost numbers higher you'll need an aftermarket gauge.