2004 V70R low boost

[motormat]

Hi There fellow R owners.

I have a 2004 V70r that i have owned for a few months. In general i love it but i have been trying to get to the bottom of a low boost issue for a while.
Can you help.

I thought something wasnt right when my 2001 V70T5 (remaped) seemed considerably quicker in 3rd,4th 5th when drag racing them (purely for scientific reasons you understand!).
I have a code reader (of sorts) in the form of an Bluetooth ELM 327 and Torque on my phone. Its been pretty spot on with all my other cars, so i have no reason to doubt it when it says there are no codes.

So i hooked a boost gauge up to the V70r to find that i'm only getting about 10psi of boost (both my reall guage and Torque report the same)
Luckily i was able to get a remap for silly money and had it done. No change. 10psi (should be more like 19 now, i know its limited in the first gears but not in 3rd-5th!)
I swapped the maf sensor with my t5 (yes i know its a differnt model). The car drove EXACTLY the same, so swapped back,
I swapped the Boost control solonoid (or TCV whatever you want to call it). No difference, swapped back.

I took it to a not particularly local performance volvo specialist. They did a leak test (no problems there), then decided to take it for a spin.

They hooked up thier vacuum / boost gauge and didnt even get 10 yards before saying "its not drawing, low vacuum" and most likely the cat is blocked and coming stright back into the workshop.

So i got a decat pipe, took it to my local garage and said fit this....they took of the factory down-pipe off and called me to say that the cat looks perfect, the cat is not the problem. I looked at it too and i agree, but im no expert.

So. What the hells next?
Could it infact be the back box ?
Cambelt slipped a tooth ? or put on slightly out ?

Any ideas or thoughts happily received!
Its drives so smoothly and nicely with so much low down grunt, if it wasn't for my comparison / boost gauge i would never have known any thing is wrong.
HELP!

[matthew1]

Vacuum leak or TCV (I know you already checked this, but check again/check it has the three vac lines in the right places). Biggest culprits.