It seems key to me that this happened after flashing, which IMO eliminates most mechanical or electrical failures in the transmission itself and points to a software issue.
OP doesn't say what kind of flash he did. Was this a dealer installed PCM update or a flash file from a tuner or a handheld tuner or?
If it's any other the latter, you need to contact the creator of the flash file and report the issue and ask for an update. If it's a dealer update, make them fix it, it's faulty (buggy).
That said, if the computer isn't telling the converter to lock up correctly on it's own, but it will lock up manually, you know two things. I) It's not an electrical or mechanical issue (ie a short or a solenoid etc) on the activation side of the loop II) the software that handles that lock up is breaking it's loop for some reason on the input side.
With regards to number II, you can't fix broken code, but you can fix broken input. So, what is that lock up code going to be looking for that might be faulty?
Engine speed (Tachometer), vehicle speed (VSS), throttle position (TPS), trans temp etc. Any of those could be intermittent or producing marginal output that the new flash code considers unacceptable where the old code did not. It's entirely possible that the new code changes the trigger levels for one or more of these inputs or that it samples at a different rate (more likely faster) and is catching intermittent input from a faulty input source.
I used software from AC Delco originally, I installed a new engine and updated the computer, and the issue arose. However, I’ve used Blackbear for my tuning needs and the issue remains, same version of the update, and I cannot have a tune created from a previous VCI seeing as my computer is now fit with the latest software.
I did some research when I first updated and found corrections in transmission pressures and misfire data sensitivity, and some garbage to do with the hands free system. Reading into the transmission side of this reflash I found it corrected shuttering/slipping between gear changes (which I could be wrong), mine would raise rpm from 3-4 if I left it in drive, but would shift fine if I column shifted from 3-OD. After the flash it worked flawlessly.
Occasionally after start up and first starring to drive the engine will cut out and pick back up, but it won’t when warm. I’ve tried to catch it through my scan tool, and I’ve recorded data through graphs but unfortunately can’t seem to catch it yet. It’s not a miss, but a loss of something like a tps, maf, etc. that kills fuel/ignition. I also have some false misfire data that reads, engine doesn’t miss, but it shows data. Mechanically it’s sound, compression and valve leak down pass, and my crank waveform was fine. Majority of it shows on 2&3 but it’ll have intermittent as well across the board. I haven’t found any broken wires that could be causing something intermittent either.. about the only sensor I haven’t watched to check for a inconsistency is the vss, that you listed above at least.
Sorry for the late response thanks for the help guys.
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