B 5.5 Passat 130 TDI, losing power/not boosting properly

[ibb]

I recently got my car back from the garage after having a new cat put on as there was a hole in the exhaust by the old one, when I got it back it was a completely different car, it now has hardly any power, the turbo does seem to come in at around 3500/4000 rpm sometimes at around town speeds, but on the motorway the car doesn't want to rev over 3000 rpm at all, the garage plugged it in to their diagnostic equipment and it came up with something to do with boost pressure or boost leak, I can't remember the exact fault code, I have checked all the pipes going to and from the turbo and all seem ok.
Does anyone have any idea what this could be?, could the garage have broken something in the turbo while changing the cat?, as it is directly behind the turbo.
I would really like to try and work out what exactly it could be, it isn't smoking and I can hear some noise from the turbo but only when revved very high and not the normal sound it makes.
Any help would be much appreciated, lastly could anyone reccomend a decent garage around Surrey/SW London that would be good at finding this sort of fault because the one I used, while good for servicing etc don't really seem to know what it could be.

[Doctle Odd]

You need to scan with VCDS and post the codes this could be a number of things not all of them expensive!

[zollaf]

as doc says, a vcds scan, but just check the thin vacuum pipe that goes to the turbo from the actuator and all other thin pipes in that area as well, just in case one has been dislodged whilst removing the exhaust.

[ibb]

Thanks guys, I will get it plugged in and get back to you, bit of a strange question I guess but does anyone know if you can get the VW diagnostic software to run on a Mac?, if not I will have to borrow a friends laptop, I'm just going to buy a cable off Ebay.

[Doctle Odd]

Buy your cable from somewhere reputable like http://www.gendan.co.uk/product_VAGUSB.html these are quite limited but a lot better than some ebay ones. VCDS doesn't work on a Mac as far as I know.

[ibb]

Right, bit of an update now, I managed to install a Windows partition on my Mac and borrowed VCDS and the cable off a neighbour, the car is coming up with 4 fault codes:

4 Faults Found
17964 - Charge Pressure Control: Negative Deviation
P1556 - 35-10 - - - Intermittent
17552 - Mass Air Flow Sensor (G70): Open or Short to Ground
P1144 - 35-00 - -
17564 - Manifold Pressure Sensor (G71): Open/Short to Ground
P1156 - 35-00 - -
17569 - Manifold Temp Sensor (G72): Open or Short to Plus
P1161 - 35-00 - -
Readiness: 0 0 X X X

I did try unplugging the MAF sensor first of all to see if this was the problem, same goes for whichever manifold sensor that goes to the back of the engine, I did reset the codes, took it for a drive and these 4 came straight back up, I'm assuming I'm going to need a new MAF and manifold sensor, don't have a clue about the manifold temp sensor or the carge pressure control though.
Any idea where to start with this?.