The dreaded Trans Failsafe Mode (again)

[Siggy]

Very sorry to post on this topic as my first post since I see it's been posted so many times but I've been through a lot of posts trying to trace this problem and I need some additional input.

2006 X5 3.0l. I'm a new owner (had it for about 6 months). The car had a lot of problems when I bought it and I've been working through them (same story as many other people, I suppose). The check engine light was on for a while and the scan said it was running lean. I felt like it needed to the Idle Control Valve cleaned or replaced and I drove it until I could find the time to work on it. The car ran smooth, no issues.

I drove it for about 150 miles the other day, no issues. Came home, went back out and when driving it the Engine Failsafe Mode light came on, followed by the DSC 4 x4 disabled and a light on the dash that said "BRAKE" came up. I immediately pulled over, turned the car off and restarted it. Everything was fine. Drove it about 5 miles and it did that again. Pulled over, restarted it, lights went off. Drove it again (trying to get home).

I will add that during this, my CD Changer now comes up with CD ERROR when I had been using it fine just prior to all of this happening.

Driving it home, it goes into Trans Failsafe Mode with no other lights on.

Runs fine, no issues with it locked in 3rd or anything, it shifts smoothly running up through the gears and doesn't appear to be any top speed locked out. No loss of power.

I check the codes and see that the Idle Air Valve is listed as stuck open at some point, so I clean that, along with the fuel bank messages I knew about. I pulled the IAV off and clean it to see if that might clear that up. I also clear the Mass Air Flow sensor with the proper MAF cleaning solution.

Put it all back together, trans failsafe mode is still there, after driving it 6-7 times (short runs), no check engine lights on. CD Player still doesn't work.

I replaced the battery about 3 months ago and when that happened, I had a gut feeling that it was the alternator, but the battery was under warranty (Bosch) and they replaced it for free even though I didn't put that battery in. Since then, I get a little whining when it's cold and I still believe it's the alternator but I can't prove it.

Right now, my gut is telling me it's the alternator, but my gut is also telling me that maybe it's the sensors detecting different wheel speeds, causing the error.

Looking for a little advice. I also put 2 new tires on the back about 1 month ago.

I'm a patient person so I'm fine with trying to diagnose it over time. I just don't want to go into full blown parts replacement mode, without feeling somewhat confident that I'm heading in the right direction. Sorry for the long first post but I didn't want to leave details out (although I might have!).

Oh, the trans fluid, when looking into the reservoir next to the oil filter is almost crystal clear. Not sure if that means anything or not but didn't want to leave that out.