I'm no turbo expert but I'm getting plenty of experance taking mine off and on. I've had this truck sense new ( fall of '98 ) '99 model and have put 224000 miles on it with very little to complain about. A few months back I experanced a loss of power but was able to drive on home at about 60-65.
My problem was a sticking gate valve in the exaust of the turbo. I freed it up and lube it and all was fine for a while. When it lost power again I though I knew where my problem would be so desided to disconnect that valve, but that did not help. Next I took the turbo off and wired the valve open but noticed I had aquired a exaust leak around the y connector where the pipes from the manifold go in. Thinking I had found the problem ( leeky exaust = no boost) I put new gaskets, new pipes, and Y ( I broke the bolts off in the old Y) and put my turbo with the wired open valve back on. Still no power. Drove it another week and the next weekend project was new turbo. Only problem was my 7.3 was a Sept '98 baby and had a small turbo and I opted to change to the larger model used after Dec. '98. Which ment another set of pipes, 1" longer each, another Y new turbo and manofold pipe. Took it all off and it would not fit on the base of the other model even though the bolt patern is the same, new one is 1" taller and the parts failed to know that. So I put the old on again and used it one more week.
Another weekend project and I have it off again and put the new base and all the rest on. Now I'm finely through. But still no power. Cranks fine, runs ok just no power. The code says no boost, but you take the hose off and at 1500-2000 rpm you can hardly hold your hand over the end. How much boost is it suppose to put out? Does any one have any suggestions? I can't even pull a trailor with it and it used to be a strong truck.
These are the Diagnostic codes I'm getting.
P0472 = Exaust back Pres sensor circuit low input.
P1119 = Manifold air temp sensor high input.
P1247 = Turbo boost pres low.
P1248 = Turbo boost pres not detected.