I agree that the prop is just compensating for low power
output of the engine.
I still think it is because we are not getting the proper turbo boost.
However, we have determined:
1. It is not the intake side (no restriction).
2. It is not the Turbo bearings (replaced).
So the next major cause would be exhaust restriction...
This is something you could do yourself:
-Go to the auto parts
-Get 1/8 inch brake line tubing (about a 3 foot stick).
-Get an engine vacuum gauge (make sure it reads both vacuum and a small amount of pressure, most do. You are looking for 1 to 3 psi, they usually go higher for measuring fuel
-Cut one end of the brake line tube off and remove both fittings (slide them off).
-Loosen your exhaust hose and feed the line down into the hose as deep as you want (your book had the distance for a good reading).
-The exhaust hose may leak a small amount where the tube won't let it seal but it should be ok for a quick test.
-Attach your vacuum/pressure guage and see what you get at various RPM.
I would hope to see no more than 2 psi.
Note: if you can not get the tube to fit and still put the hose on the exhaust outlet. Maybe you can just install the hose about 1/4 to 3/8 inch on the manifold (so it is barely on there) and clamp it good at the edge. Then you can make a small hole in the hose for your tubing to be inserted. After the test you just slide the hose all the way onto the manifold and the small hole won't make a difference since it will most likely be under the clamp anyhow.