Refer to post #5134 on this page
http://forums.tdiclub.com/showthread.php?t=452221&page=343
It isn't the cat.
So let's see: if the intake manifold was clogged, then I'd get instant boost pressure, which I don't. The actuator works, holds vacuum. Ditto the vacuum line to the actuator. All there is left is the N75 itself, and the turbocharger itself - clogged turbine section, or slow N75? I do have a good N75 with which to compare, so I need not try the N18-N75 swap. It does not appear or sound like the EGR anything is leaking or cracked anywhere, either. Oh, and the MAP sensor is different since the intercooler problem. But I still have the old one.
Oh, the fun. I've an Audi timing belt on the schedule first though, so the drama will be extended.
Cheers!
PH