Hi O850,

I too have a 1992 965. All kinds of trans shifting difficulties and flashing arrows. The wrecking yard (PicknPull) provided from a '93 960 a TCM and read diff speed sensor. No change. Speedometer now indicating all over the place or at 0 mph.
Reading around I came across this write up:

https://www.brickboard.com/FAQ/700-900/ElectricalSpeedometerRepair.htm

The 1991-1992 740/940/960 speedometer are interchangeable. The "Yazaki"...
I found a donor speedometer out of a '91 940. Bought replacement capacitors online. Using Davide D's (Thank you!) write up I was able to complete the cap swap. Pulling the speedo from my 965 I looked at the four capacitors and you could tell they were bad. Electrolyte had made a mess of the circuit board and under the chip. Apparently, there were a whole bunch of faulty capacitors shipped and installed in the 1991-92 740/940/960 models.

The job was a little intimidating at first- but following the steps got me through the repair.
I don't recall if there was a 311 code. My indications were the flashing arrow and a 232 code.

I'm always on the lookout for another 1991-92 740/940/960 speedometer as a backup on the the shelf.

Jeff