loss of power after minor service 1.9TDI PD

[dtr]

My Toledo 1.9TDI has been in for a normal minor service and had intercooler seals and wishbone done at the dealership. The car now has a lot less power at low rpm range, and first gear is particularly slow and needs significant revving to do anything faster or go up a steeper hill. 5th gear now needs flooring to hit 70. Braking performance is also down.
The dealer is convinced the car is absolutely fine, rechecked all repairs and found nothing 'wrong'. I would be wasting time going back yet again to the same branch, and it wasn't cheap either.

I only have OBD dongle with Torque - that can see nothing wrong. Turbo boost went up to 15psi (if that could be trusted at all - at least we know turbo does something useful) at 50mph, and max bhp was reported 67 (got up to 55 in 4/5th) so about 55% what it should be.

Where would I start sorting out my car and ideally making it better like it was - pretty good but nothing amazing? Lowish mpg (40, never above 48) was my major gripe so far. I think I need to finish the business with dealerships and expensive but not always reliable or helpful garages. Not a single one even wanted to hear anything about fuel consumption. I'd like to eventually learn it myself, at least the computer diagnostics and standard service.

Thanks in advance for suggestions.

[zollaf]

loss of power and loss of braking performance ? what connects the 2 together, the vacuum system. this powers the servo and operates the turbo, so a loss of vacuum can give poor performance and a hard brake pedal. so, i suggest you look over all the vacuum pipes from the tandem pump that makes the vacuum, to the servo, and all the smaller pipes that operate the turbo and egr etc..
i am fairly sure you will find one has been dislodged or chaffed through.

[dtr]

Thanks, I did suspect something similar and asked the dealer to look for this with no results. I am happy to accept that they missed it.

I am fairly new to self-repair and new to VAGs so I don't really know where to find the parts in question (embarrassing, I know). Are there any clear schemes and / or manuals to help me with that? Once I found such split pipe on a merc, but that was more sheer luck.