'98 LeSabre Juttery Trans issues.

What is your question?

When I accelerate at any speed it seems like the trans goes into seizure mode and starts to jutter violently until it shifts into the next gear available then It's fine cruising until it downshifts or takes off again, then back to square one. It isn't slipping, (Only raises about 400rpm on brake test) and 0 codes are being thrown for any drivetrain components, and it shifts flawlessly smooth. The torque converter was a brand one from Pro-King 10k ago. That's my only guess it that's defective. Fluid and filter were changed 3k ago. Fluid, CV Shafts, Trans/Engine mounts and alignment are all fine. Any suggestions?