vacuum test HELP

[pachanga231]

had this problem previously, on the motorway at about 70/80 mph the car lost power. after some messing it was all pointing to VNT vanes being clogged/stuck but on a whim i swapped the thrust sensor and bingo all was fine. prior to fitting the thrust sensor i also changed the n75 but it made no difference. so both of these sensors are newish.

last few weeks its been playing up again intermittently, only at high speeds though but this time its not POSITIVE BOOST but NEGATIVE BOOST it comes up with this fault;

1 Fault Found:
17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-10 - - - Intermittent

on the wiki the only thing left is the VNT vanes but before i get the the turbo removed i want to be sure that its the vanes. i do have vagcom but dont know how to properly test the actuator rod or do the graph thing etc etc. want to cancel out all possibilities

could someone please help me out with this .

TIA