First of all, many thanks to all the fine folks on this board that provide so much valuable information. I have been reading (there is a lot to read) as much as I can about the 6.0 and how to maintain and improve it.
Update on VGT:
Problem may be solved. Code was "turbo underboost". Dealer fix was replace the VGT with new improved version that does not rust. $2500. I was reading many of the issues on this forum and yesterday I decided to try a EGR disconnect. Wow! I have a new truck.
Prior to disconnect the turbo psi would only boost if I went full throttle and then it took 4.5 seconds to engage. The power always felt like a snail in mud and fuel economy was 13.4 best possible.
After disconnect, the psi gauge shows some involvement at all speeds and bounces to 30 psi at full throttle with only a very slight delay. The truck is very responsive and calculated MPG is 15.4 at 65 mph. It seems like this diesel/vgt combo was designed and built to run this way, and that maybe the EGR setup was an after thought to meet epa standards. Anyway, I have a totally different truck right now, and time will tell if this is a permanent fix.
I hope it is ok that I did not post this in the rather massive EGR thread, as I thought it was applicable to this discussion.
One disclosure that may have affected the large prior and current performance differential is that I have 35 inch tires but the speedo and shift points were adjusted by the dealer.