That'* what my friend he'* a Tranny specialist, that'* all he works on, well he used to be a Mecanic at a Chevy dealer but he has his own shop. But I let him drive my car and right before it shifts into overdrive, it will downshift for a split sec. and then will shift back into overdrive, he said the locking in the torqe converter is short of shaking back and forth, something like that, I didn't understan what he was talking about, but he said he could get the part for $60 bucks and total for parts and labor is $200 bucks. He also said it did it to his Lasabre, the same thing. Well I hope this helps, cause I know what your going thru.
1996 Bonnevill SE Series 2.
203,000 Miles on it.
NGK V-Power Spark Plugs. Taylor 8mm. Spark Plug Wires. 180 T-Stat. Custom CAI Intake.