i haven't had to mess with a tiptronic yet but here's some tests that you could do that are from the porsche electric workshop manual; perhaps they can be useful for you. ive heard changing the oil&filter in there solves some guys problems too.
id try out the trans oil& filter change just for the sake of it & so you can inspect the fluid for anything nightmarish but id also do those tests just so you can go through the system with the muilitmeter to confirm or eliminate anything.
i have some bits to the electric workshop manual so if your maybe looking for a page get at me
a little off topic, i got a 01 986 s that im working with that has a misfire i cant seem to peg; yet anyway. i posted a thread on it a couple nights back under 7.2 DME imput signals. i was seeing if you can perhaps help me out with sharing some data of your actual values& imput signals; it would be cool to have another cars values for comparison
get at my thread if you can