Shimmy and vibration while accelerating / under load

Sounds like the clutches in the tranny are shot and it needs a rebuild . You've dumped all that money into a 23 year old car and now you either keep fishing or cut bait .

I do all the work myself, additionally and at the same time I teach others to do this kind of maintenance, so it's not that bad. I own several late 90's / early 2000's GM vehicles with the 3800 / 4T65E. Probably the best vehicles GM has ever made in the modern era. My limitations are with transmission diagnosis outside the capabilities of my OBD. So, off to an expert later this week. I love driving 20+ yo BOP's.

These transmissions are notorious for losing overdrive and TCC lock in. There's a shaft inside the transmission that wasn't made correctly and the splines break off. Usually the only symptoms are no overdrive or TCC lock in and sometimes a whine when the transmission is supposed to shift into overdrive. You could also be looking at a bad valve body. I had an 02 Impala that would jerk and bang and that's what it was. Luckily it was still under warranty. Hope that helps! Jim

Thank you James for this information, I am gearing up to replace the transmission. During disassembly, it was identified that the output shaft (where the CV axle meets the transmission) on the left side of the transmission has significant play. I'm thinking this is my problem. I'll soon know.

You're welcome. Glad to help! Please keep us posted. Jim