2000 BMW X5 BMW X5 4.4i V8 (03/2000) problems with transmis

Transmission problem
2000 BMW X5 V8 Four Wheel Drive Automatic 118k miles

I have an issue with recently bought X5 4.4i V8 (03/2000). Now it is appearing as a series of symptoms spread over several components. My biggest concern is transmission.
Under certain conditions (e.g. when slowing down on lights or drawing in the jam, at the very last moment before the car stops completely) it is unecessarily downshifting 3>2 or even 3>2>1). Sometimes it's quite roughly, especially in D - Drive automatic shift program. It is less appearing in S or M mode and I can't remember it ever happened in the first 10 minutes after the cold start. On the contrary, my suspicion is it was worsening in due proportion with raising temperature in the engine compartment (although engine coolant thermometer always remained in a propper position).
The other, for me less annoying symptoms, are e.g. false check control and onboard computer messages (check rear foglights) or sudden PDC malfunctions (starts to operate when shouldn't, with confusing PDC tone soundings).
Shortly I've acquired the car, I've experienced a few other issues, which maybe were a predecessors of my today's troubles. It began with several CHECK COOLANT LEVEL messages and culminated when the shaft of the ventilator fan got broken), which was resolved FoC at the BMW repair shop, where I bought it (whole ventilator and cooler radiator should have been replaced). Disruptions continued shortly I took it back and I observed the first strange behaviour of the transmission in low speeds. It was clearly unussual and I've been "awarded" even with TRANS.FAILSAFE PROG and LEVEL CONTROL INACTIVE messages and gave it back to the repair shop.
Now the car came back with status "we tried everything - replaced the instrument cluster, re-loaded every piece of SW and applied all required fixes, verified it's all in most current versions and from standard diagnostic tools we can't getn neither any sign of problem, nor any relevant information or indications where a hidden cause of the problems could lie, now we can only wait until BMW in-depth car IT gurus will be available (promised for mid of January 2010) to let them discover and resolve the voo-doo..."
After I did a bit of research over the web, my feeling is there is something wrong with the cooling, the sensors, or the way involved systems exchange (sends/interprets) the temperature related data. I also believe my case has a lot in common with the problems described by a guy using nick moneytree, where the feedback was provided by Dr. Hagerty ("2002 BMW X5 Transmission shifting problem v. specfic" started at Sat May 24, 2008 5:32 am, link: http://www.2carpros.com/forum/previous-vt137969.html?postdays=0&postorder=asc&start=0&sid=da8ad4ccd797283314826d84012596ba) and many other unfortunates with the same or similar long lasting problems with BMW automatic transmission I found on the forums and discussions...
I will really appreciate any advice or suggestion. As I can't believe such issues were not resolved already, a link or direction to required information/source dedicated to the first generation of X5 4.4i V8 model would serve me the best. :-)
Many thanks in advance!