Tiptronic Not Shifting
 

The car is a '98 2.5l tip with approximately 75k miles on it. Initially I experienced hesitation at low RPM (2k to 2.5k) which I have attributed to the vario-cam. Recently, a more serious and troubling issue came up.
When cruising at mid RPM in 4th or 5th gear (D-mode) and flooring the pedal results in a kickdown to 3rd, rapid increase in RPM and acceleration, then a slight hick-up/hesitation at 5k RPM and then all the way into the redline where it sits without changing up to 4th. The RPM stays at around 6K until I lift my foot off the accelerator pedal before it actually decides to change gears. This feels serious and not right...can anybody offer any advice.

There are a number of things it could be. With 70k on the clock, you're likely to need a filter/fluid change - if the fluid level is low (no way to easily check), this could cause shifting problems, esp. at high rpm. When you look under the car, is the gasket line of the tranny pan leaking? If so, you're will be down on fluid... how much is anyone's guess.

It's not likely to be the selector switch - how does manual mode work?

It could be the hydraulic control unit, but this goes beyond DIY for most people.

I would change the fluid/filter and see how that affects it's operation.

Beyond that, get it to a dealer for a proper diagnosis since there are so many possibilities for what you're experiencing.

Manual works perfectly. Its in auto mode under hard accelleration when I get trouble. Under normal acceleration it works fine though, except at low-ish rpm (2k to 2.5k) it won't go into 5th easily. I will check the filter/fluid when I get a chance and post a response...thanks for the help.