While searching for something else, I came across this TSB that seems to fit your condition, except it'* listed for the L36. When my friend'* 00 SSEi was experiencing this problem - the TPS swap didn't change anything. Hopefully, it will in your case.

Interesting, Dick. Maybe those guys are onto something over there.

I'm hoping this corrected the issue. I'll tell ya - the new unit was just as clean the 105,000 mile one I replaced. Hard to tell visually if there was anything wrong.

Did your friend ever come to any resolution with his SSEi?

Turned out to be a grounding issue, with a corroded grounding strap to the floor pan from the negative battery terminal. Cleaning that up solved the problem. Apparently "dirty" DC power can cause all kinds of strange problems to pop up. That was the only symptom, too. It happened mostly at highway speeds, with TCC lockup and in overdrive. Slight acceleration (like climbing a hill) without a down shift would cause the jerking, and you could see the tach vary about 200 RPM every second or so. Tuneup, coil and ICM swaps, TPS swap, tranny flush, etc., had no affect. There'* a TSB for the TCC lockup solenoid, too...but the symptoms do not sound quite the same.

Wow! What a find!

I'll have to check the grounds coming off the negative battery terminal. I'll clean them regardless.

If the TPS doesn't correct the issue I'll do my best to return it to AutoZone. It'* $55 I can put back in my pocket.

When all else failed, I decided to take a tip from the 90'* group and check the battery connections. Those attached to the battery, under seat and under hood connections were all fine. When I pulled the negative cable where it attaches to the floor pan under the seat, the threads on both the bolt, and in the pan where pretty rusted up. I cleaned them up as well as I could, scraped a bit of paint off the pan, added a star washer for some extra bite, applied dielectric grease, and it'* been fine since then. Good luck. In my case it helps to have virtually identical cars. Parts swapping is cheap.

It makes me wonder if the Buick has the same grounding location.

Was the ground found underneath the passenger or driver'* side front seat?

Is the battery under the rear seat? That'* where it is on the 00+ Bonnevilles. So, the negative battery cable is rather short. It goes from the negative post of the battery, to the floor pan under the seat. Battery

No, it'* under the hood in the Regals. Passenger side front. Conventional GM location.

May want to check the connections anyway.

Tell you what helped my 96.
I tweaked the voltage setting on the plug and play TPS to the center of its range at idle by filing the holes and making it adjustable.
That and installing a tranny cooler as it seemed it only happened when hot and the fluid was thin.
I think its a combination of the timing off from a TPS out of range and the thin fluid.
Don't think you will need a tranny rebuild.