So here's the deal... Did the first rebuild on my C-15 (6NZ) recentley at 800 000 Miles, and 35 000 hours.. Worked great , just was pressurizing the coolant (due to a blown head gasket, which was due to a cracked sleeve) Replaced everything but the injectors water pump and oil pump. I have only put about 500 kms (200 or so miles) on it since getting it back, but now it seems to have a little bit of a "flutter" in it. bThought the vales may have seated so I had them reset with no change. Before the rebuild I use to be able to get 40-42lbs of boost easily, now I can only get 30-34 and it takes a little longer to spool up. Any ideas on what the issue would be? Im thinking sticking injectors, but the cut out test didnt really seem to reveal much.

 

Do you have ET??? Attempt to do a timing calibration procedure.
What all parts were changed and did you use Cat parts or aftermarket.