Revisiting my 6000rpm cut-out problem - '95 S6

[Bob Rossato]

Ever since I bought my '95 S6 last year I have had a problem with the engine
cutting out at 5800-6000 rpm, instead of the 7200 rpm redline.  It just
feels like the rev limiter engages.  Engine pulls like crazy then hits a
brick wall and refuses to go any higher than 6000 rpm.  I haven't had the
opportunity to deal with it too much yet.  But, I have some performance
enhancements piling up in the garage and more in the pipeline, and before I
install any of them I want to get the car operating properly in its stock
form.

Car has 43k miles on it.  New F5DP0R plugs were installed when I bought the
car and have 8k miles on them presently.  I have checked them and re-torqued
them a couple of times.  I did replace a failed BPV shortly after I picked
up the car, but nothing has changed.  I checked the Michelin man hose and it
looked fine.

This weekend I installed a temporary 25"hg - 0 - 30psi gauge to finally get
some readings, but having very little history on these cars I need some
calibration input from the list.  At idle it runs about 15" hg vacuum.
Normal part throttle, maintaining constant speed, it reads 10" - 15" hg.
Light acceleration about 5 psi boost.  Full throttle, sometimes 10-12 psi,
though most times 13-14 psi boost.  It will hold max boost all the way until
it hits the wall at 5800 - 6000 rpm.  I've only checked full throttle
readings in 1st - 3rd gears as the roads are pretty congested around here.
I have the gauge "T"d off at the ECU inlet via 10-12 ft of 5mm dia nylon
tubing.  I wouldn't expect the length of tubing to impact the max pressure
readings as it's obviously dead-headed.

How do these vacuum/boost readings look for a _stock_ S6?

Though, even if the boost levels are off, I can't see those affecting the
redline.  I should still be able to go beyond 6000 rpm, and a leak in the
intake would not manifest itself as a sudden cut-off.  Right?

What else can cause the ignition to cut out early?  Are there any sensors on
the AAN that, if faulty, would limit rpm's (similar to the inlet air temp
sensor 4k rpm cut-off on the Urq)?

If it isn't a sensor issue, I guess the only thing else left would be the
ECU.   As best I can tell the car has not been chipped by a previous owner
(the carpet seam had not been cut and there are no signs of the box being
opened).

Any other suggestions?  Sprinkle some holy water while shaking some chicken
bones perhaps?

Bob R.