How you getting on with this? Did you try unplugging ABS sensors or reading codes?
Your theory on sticky release bearing seems a good possibility to me.
A couple of years back my gearbox was occasionally dropping into N when cold -
SEE THIS POST
As Conaero kindly told me on that thread, the standard PIS setting is around 4.19. Mine, as is yours, was at 3.93 so had been changed by someone to get faster shifts.
I'm thinking as the cutches get older the release bearing starts to get a bit sticky, and as the PIS was set so low it doesn't get to move a great distance so is on the same bit of shaft, so gets even stickier.
Increasing the PIS puts it onto a 'clean' bit of shaft and when operating, moves a greater distance, which frees it up a bit. At the time I had to put mine to 4.30 to get the car to drive faultlessly and until this wheel speed sensor issue its been faultless. My wear Index is 4000 which I believe is within range as I read 3600-4000 is where they should be.
Now, I might be misunderstanding how this all works and talking absolute b*ll*cks, but in my head it makes sense. lol
I'm not saying this is what's wrong with yours, as you have different symptoms, but an experiment with the PIS settings and gearbox re-learn is an easy place to start before you get any deeper.