stormlover
Adventurer
Just my two cents. I have found that boost in a diesel is usually a good indicator of overall performance of the engine. I have found that low fuel pressure can cause a boost concern. I would check fuel pressure, if you don't find any leaks. Generally low fuel pressure will not cause a code or much of a symptom on a 6.0l other a little white smoke and/or lower boost pressures.
Crabby did the blue spring upgrade so he should be getting 65 psi or so. A fuel pressure gage and pyro are the two gages I have that I added that the Scanguage doesn't monitor. No pids.
How about the up pipe? Any chance it's not mated just right? Sounds like you still have a leak somewhere.