8L45/8L90 teardown videos from Transmission Digest
 

Part 1: https://youtu.be/RUfw3lS4H-Y
Part 2: https://youtu.be/cRYw3Gx13yA

Just found this very interesting education material and thought I'd share. They mention several design changes, including one to the stator support to address delayed engagement ("clunky shift") issues. My 8L90 seems to be a newer unit, because it never had that problem, even before the first flush and the custom PCM tune I'm running.

Yep, glad I got the extended warranty. Is there a tcm recalibration that dealers can do to clean up the shift quality and other abnormalities in these 8 speeds?

I don't think so, at least my service manager and the senior tech who works on my car at the dealership have checked several times since late 2018, early 2019 and there have been no updates. They gave me a printout last time with the current versions, I can check the one for the current TCM calibration if you're interested.

Most likely no programmers at GM work on refining this transmission anymore, they seem to be running down the clock and hoping for a low warranty concern rate.

You will have better luck with an aftermarket tune once your extended warranty expires, my (impeccable) TCM tune is from Jannetty and I know there are several other reputable tuners as well who have the 8L90 figured out.

Well, I can't say I blame them honestly for waiting it out. Seems one of the main issues is slow clutch fill times attributed to the piston designs and calibration (both I'm guessing could be fixed/updated if needed). But I'm sure GM won't ever foot the bill for all that.

I would be interested in comparing my tcm calibration to another current version. Should be no harm in just downloading my tune to my laptop as far as warranty purposes go right?

The tech needs to do the clutch relearn procedure correctly. Between the relearn and the fluid flush the 8spds in both my 2016 camaro and 2017 Yukon work very well.