I have a Passat TDI 130 that has over boost problems. The car has done 200,000 but is a belting motor (just getting run in) about 3 months ago I had the turbo off and cleaned the vanes (and what a work of art that was) there was a great deal of end float in the main turbo impeller so a good quality replacement was sourced. This reduced the amount of smoke out of the exhaust and is now down to barely nothing, I dont use hardly any oil now compared to before. The problem lies when I take the car out of town and local running and put it on the motorway. In 6th gear the turbo over boosts at 2500rpm in 5th it will always over boost at 2800 and in 4th it will rev past 3000rpm (but I dont really want to thrash it). 6th gear at 2500rpm is about 75mph and returning 55mpg I am happy with that. I have contacts in the motor trade and have tried the car on 3 different code readers (Bosch KTS, Snap On Scanner, Some Pico tech software) and they all come up with the Over boost fault code. A neighbor of mine is a parts lad at VW and got me the part at trade (he said it is always that that goes on them, we fit loads) it bolts to the front of the engine and has the 3 vac pipes going to it with an electrical multiplug connector on it. This has been on for about a fortnight now and is no different. I have been altering the actuator arm length, took a measurement with a vernier calliper (recorded it) and adjusted it, but that has made little difference and have returned it back to its original length. I was thinking of replacing all of the vacum pipes this coming weekend but thought I would post on her to get some ideas and inspiration.
I hate it when the turbo drops out it is so lethargic its like superman and Kryptonite. Any suggestions gratefully appreciated.

Is the wasregate working?
If the diafram (sp) has split inside the wastegate then the wastegate will be staying closed and causing overboost

Just a thought

beat me to it.

Id also check the vacume pipes a small leak will cause it to go like a train a big one will cause it to feel like a bag of poo on the end of a long rope.

Typically it's the Solenoid valve (3 hoses) that once failing leads to overboost.
But if yours is New?
Possibly the Turbine Ratios on your replacement Turbo are ermm... different it's fairly easy to get an incorrect one UNLESS it's a direct from the VW dealer replacement part.
Wastegate actuator 'could' be broken but even a ruptured diaphragm (test it by sucking on it's vac line.) Will not necessarily give over boost as the ex pressure will often overpower the wee wastegate 'keep closed' spring.

And check if the ECU needs fault codes re setting as it may assume an overboost problem is still there and restrict the use of it, maybe, just a guess

A company called Inertec now produce a turbo cleaner for the variable vane turbo's , saves having to remove and strip the turbo. You just disconnect the exhaust and use 1/2 an aerosol into the turbo, leave it to do it's stuff spray in the second 1/2 and then flush it out. Haven't yet used it but if it is as good as the rest of the companies products it should do the job. Could be the wastegate not working causing your problem?