Have you checked the boost pressure regulator/control valve is working? I can't see any mention of it in your posts.
You could use your vacuum pump to control the turbo.
The turbo doesn't appear to be boosting, which as Fiachra has said could be an exhaust blockage, but could also be the boost control valve. (They do fail quite often).
Also, have you checked that the turbo actuator is moving?
Regards, Andrew
Ps, most td4's "misfire" at around 2200-2500rpm.