Kickdown and Speeometer questions re: Audi 100

[Einhorn Hofmann]

Got my car from the transmission shop last night.  I noticed that at
wide-open-throttle, it doesn't kickdown unless the car is under about
35mph.  The pullrod from the throttle assembly and the push rod to the
transmission all appear to be adjusted correctly according to the Bentley.

Just wondering if this could signal something wrong inside the
transmission, or is kickdown at wide-open-throttle purely controlled by the
adjustment of the linkage.

Today I was driving and the speedometer started to bounce, A while later it
went flatline.  This isn't the standard "bobbing speedometer" which I'd
experienced years ago, known to be caused by a micro-crack in the solder on
the instrument cluster.  I repaired that with with enough redundancy so
that it can't be the problem.  Also, the pattern of bobbing was much
different with the known "bobbing speedometer".

The question I've got, where does the speedometer get its signal from?  Is
it from the plug on the side of transmission as I suspect?  I know from
performing ECU diagnostics that the car has a "transmission speed sender",
but I thought that this just sent signal to the ECU.  Does it infact also
feed the speedometer?

Sorry for the clueless questions, I've no BTDT on this area.  I'll be
calling and returning to the transmission shop as soon as I can, but I
wanted to know as much as I could about these issues first.

Thanks
MC