Mine was doing the same thing... Sorry to say but you probably have blown head gaskets. Mine would run fine around town or unloaded but as soon as you started leaning on it hard it would puke coolant. About 2-3 minutes into a big climb it would lose power, EGTs would go way down and so would boost. My opinion is that the gaskets and/or bolts had been compromised but would seal until things heated up to a certain point. Once that point was reached, something would move such that the gaskets would no longer seal and I'd be stuck crawling up the hill. Would reach the top, back off, and a couple miles later everything would be back to normal boost and power (until the next big climb). I called a number of dealers in town until I found one that would install some ARP head studs (that I furnished) during the warranty repair for an additional $200 in labor. By that time the motor had ingested enough coolant so that the turbo had gotten gummed up, so they cleaned that out as well. Last trip with the repairs went very well, truck pulled great and didn't lose power even on a very long climb.
Good luck!
-Brian
Good luck!
-Brian