I know this is far late for a reply
i have a 94 i bought new in 93
also bought the 5 year 75k extented warranty
about 16 months old it started not going into overdrive when i was on the road for 30 minutes or so
dealer never coul d find anything (so they say)
then 2 months after the warranty expried
low and behold they say its my transmission and it needs rebuilt
yada yada
did not fix it
2 years later same crap excuse from a transmission shop
another wasted rebuild
FYI
in about 95 or 96 (while still under warranty) GM released a recal
turns out a bad design
coolant lines to the trans. were undersized
when it gets warm it cant cool enough
then locks out the overdrive
so dont pay anyone for a rebuild etc
they just want your money
just upsize the coolant lines and it will fix for most people