7020 loss of power

My first thought was pump or timing, hard to believe two pumps make it act the same.  Since you checked good fuel delivery, and the turbo won't affect RPMs much under no load, what fuel is in it?  Filters?  What does it do, if you prime it while running?  Could it have gotten some gas in the diesel, I am sure you are aware white grey smoke is typically unburnen fuel, suggesting spray pattern or pump problems.  I am at a loss, hopefully you will get some better ideas from others.

Well If you have one laying around, then yes, but I don't know if I could bring myself to spend the money on mine to have the pump reworked just yet, since it exhibited the same exact symptoms as before even with a different pump.  Yes it was a used pump, but from what I read you know that pump, how did it run on the tractor it was on, when it was removed?  Yes pumps can die in storage if they are weak already, but I would find it hard to believe the exact same symptoms were displayed.  It's possible, it really does sound like fuel delivery, especially the "won't rev part"  Even an engine that is out of time a few degrees retarded will still rev properly, I have never found one too advanced to know what happens, but I would imagine it could handle a few degrees, as long as it wasn't under load.

put a pressure guage in the intake manifold (intercooler) to make sure it's building boost. Could be a blown intake gasket, or a plug has fallen out somewhere allowing all charge pressure to escape. Seen it several times on 301's!

Put a vacum gauge between pump and filter with a clear plastic line. Check for air in fuel and vacum draw at full rpm.

 If it is one with electric fuel pump it should show pressure.