4EAT slips bad after second fluid change...

[91Beater]

91 200k miles
I replaced the fluid when I got the car a few month ago.
No issues for a while.
Pan started to leak, so I removed the pan and replaced the fluid. I got code 12 from TCU.

The RTV leaked, so i did it again using a gasket. For one reason or another, code 12 went away but transmission still slips like hell. I don't feel the shift at all now. Before this started happening, it shifted pretty hard from 2nd to 3rd.

So WTF? Did the previous owner have some band aid additive like Auto RX, Lucas or Seafoam?
I'm not about to commit to major work on this car. Which additive should I give it a shot?

[Legacy777]

Did you add the correct amount fluid to the transmission? How did you check the trans fluid level? The car needs to be running at idle, at normal operating temp for the trans, and parked on a level surface. Slowly cycle the gear selector from P to 1, and then back to P, then check the fluid level.

[91Beater]

Did you add the correct amount fluid to the transmission? How did you check the trans fluid level? The car needs to be running at idle, at normal operating temp for the trans, and parked on a level surface. Slowly cycle the gear selector from P to 1, and then back to P, then check the fluid level.

Yep. Did that. It was still slipping like crazy. Delay engaging into 1st after stopping.

I added a 24oz bottle of Lucas Stop Slip. Still not as ok as before, but drivable.