Sorry folks, I didn't mean to abandon this post. Somehow it just flew under the radar.
Looking at the timeline, I started this discussion shortly after buying my M56x. When I bought it, I hopped on the highway and headed straight home on the highway so there wasn't much to notice in the shifting issues.
Over time as I drove it in town I experienced what I thought was a transmission flare somewhere between 2-3. For manual transmission drivers, this felt like when you're shifting gears but then push the clutch in slightly. It mostly happened while creeping along and then trying to go back up to speed.
Not all the time did it happen, but when it did, those were the conditions.
Starting from a standstill did not show any issues. Shifting in manual didn't show any issues either.
It was a minor annoyance to me that nobody else in the car could even feel, so I just let it be. Once while at the dealer, I asked them to change my fluid and reflash the TCM.
I can't remember exactly how the reflash went, but I feel like they didn't do it and neither did I push for it. I wanted to isolate the solutions one-by-one and if the fluid change didn't work, I'd have gone back to pay for the reflash.
Looking back at Mickey's link
I wonder if a deeper dive would have shown bad solenoids as well. As much as I remember asking specifically about the fluid condition, they said they didn't see any issues. Part of me wonders how well they paid attention to that stuff. Oh well.
Unfortunately the new fluid did absolutely nothing for the issue, but since it was rare and not severe in occurrence, I kept living with it. Honestly, the only reason I could feel it was because I had another M56 to compare it with.
To clarify, yes the fluid did nothing for the car - it made it neither better nor worse. I don't ascribe to the notion that
"you shouldn't touch your transmission fluid if it has never been touched."
You're probably wondering if I ever found a solution.
Well, yes, but I can't exactly replicate it .
Remember back when we all started getting anxious about the failures related to the high pressure fuel pump and started digging into it? That's the first car I replaced the HPFP lifter bucket on.
I did nothing else to the car around that time, but all I know is that when I went to work over the next few weeks, the weird flare was gone! It was also sometime in November and the air had started cooling off a little.
Coincidence? Perhaps...but since the issue seems to transcend beyond V8s, then I can't say it's a HPFP issue.
Also nobody else has mentioned any variation in behavior dependent on weather changes, so I'm going to have to imagine the car had a mind of it own. I would like to entertain the possibility of bad solenoids, but I know that such issues don't fix themselves.
Sadly, I'm never going to find out. The car was sold a few months later, having given me zero driving problems through the few months of winter.