Not familiar with that specific trans,
does it have a speed sensor/s on the trans ?
could be something simple like that & overlooked
computerized stuff is weird or more hard to diagnose,
if they don't know the stuff, or just too lazy to do the protocol,
research/diagnostics, plug into the OB2 port, for codes
I wonder if there's an update for the computer/flash a new program
most GM trans that had computer aid, can be flashed/changed
a good dealership, good service writer/shop mngr & 'competent tech' should know
Or buy/get a aftermarket programmer/flash it with a upgrade/performance deal
(if it's not locked out so you can't work on your own, BS govt. EPA/C.A.R.B. crap)
or use an OB2 reader, & *see what codes pop up or needs to be cleared,
the *latter should tell the story, how you interpret it, to fix it, is the other part
do a trans fluid & filter (maybe partially clogged ?) change, both,
maybe a flush (?) too prior, it's not that tough
it won't hurt it w/33k miles either, it's almost due anyway
use the right fluid
I'd also wonder if line pressures are off, or a band adjustment (don't know the trans)
or when cold the front pump, not keeping up takes a bit to catch up
sort of like the old 727tf need to check it in neutral,
so the pump is fully working
or when sat for a long time after it's 1st fired up
need to put it neutral to get the converter full & pump working correctly
before taking off
