I've been tuning & modding GM cars for 6 years and the only time a warranty was canceled was when a C6 owner changed is own spark plugs at Cox chev here in Bradenton.
Otherwise I have yet to have a customer, or talk directly to one tha had GM go into the PCM to look for a tune flash. I'm sure they do with caasrophic drivetrain failure, but it takes far to much effort to check every car in for service.
Here is a good thread looking for anyone tha has experianced wha you are so adamant happens all the time:
http://www.camaro5.com/forums/showthread.php?t=104741
I don't know how else to say it Tracy. My tranny has been replaced. GM doesn't care as long as it's not abused and that's hard to prove on a tranny. If I turn it up to 7000 RPM and blow the engine now I got a problem. I'm just trying to help some brothers with info but I'll quit.
Also remember GM asked me to flash mine. A dealer cannot modify a program.