Intermittent Boost Problem
I have already solved this problem, but I wanted to post in case anyone else ever runs into the issue.
I was having an intermittent and extreme loss of boost. For example, for half of a 30 minute drive the truck would be fine. For the second half of the trip I could not build more than 2 psi of pressure. If I stopped, turned the truck off, back on, and continued on my way... it might be back to normal or it would continue to lack boost, 50-50 chance. Seemingly random.
Solution: I had developed a loud exhaust rattle many months back before the boost problem cropped up. I thought nothing of it, wasn't concerned, and was in no hurry to fix it. I never would have thought the two problems were related. It turns out that the catalyst in the catalytic converter had broken loose inside. It was bouncing around freely and about half the time it would become lodged on the output side of the catalytic converter housing. This created such a restriction in the exhaust path that there was hardly any flow. No air out equals no air in. One symptom was that the turbo sounded as if there were a leak on the charged air side. I had a shop do a diagnostic with their IDS. Everything checked out fine at the time. Installing a catalytic converter delete kit or, as I did, removing the catalyst and reinstalling the stock pipe solved the problem. I also suspect the Exhaust Back-pressure (EBP) sensor may have indicated a restriction.