I have just reinstalled my rebuilt turbo on my 6.0 powerstroke. I am not getting the correct boost and I am hearing blow by or an air leak. It is coming from the turbo itself. When I disconnect the VCT pigtail the blow by stops. All the boots are tight, the down pipe and x pipe are connected to the turbo correctly with no leaks. Any suggestions? Or just tear it back out and take it back to the rebuilder?

I suspect there's a problem the rebuilder missed. Personally, I would return it, buy a new Motorcraft turbo, and start using full synthetic heavy duty diesel oil.