I've searched a few times and keep coming back to these two threads:
topic285809.html
auto-transmission-manual-mode-issue-t454533.html

But neither one seems to definitively describe the problem I'm seeing in my 2008 G35x:

- Some time after starting my car, I can put it into "DS" and it will probably stay there for awhile if I leave it.
- If I put it into manual, usually by forcing a downshift, it will happily oblige.
- Minutes later (sometimes not even) it will return to "D".
- It will not return to Manual mode until I restart.

Over the past year, I have observed:
- Worked great for awhile after a recent (scheduled) transmission flush. All fluids replaced.
- I'm not positive but I think it's related to transmission temperature. If I use it hard, it usually seems to happen faster. Sometimes, one downshift is all I get.
- I've seen one time (and one time only) where I shifted over into manual and it stayed in "D", but the 2nd time I tried it went to manual.

I'm inclined to hope that, loosening/tightening the 8mm bolts may address the issue. It's my fear that the transmission can't keep itself cool enough to function. I'm considering selling the car soon, so I'm wondering if anyone else (recently) has had and resolved this problem with their G35/auto?

Hmm...I've driven mine quite hard in DS mode (TOTD) and never had any issues. The only time I have the vehicle go into manual mode and then drop back to normal mode is if I use the paddle shifters without moving the stick to DS. This is completely normal.

If you are concerned about transmission temps look at adding a bigger or additional transmission cooler.