If your issue is between shifts, that is not torque converter shudder you're experiencing. To my knowledge shudder only occurs during the lock up phase of the converter which is usually around 45-60mph and light throttle input.
If you're experiencing a thud or shudder during 1-2 or 2-3 upshifts, that is clutch plates and/or bands or possible servo and solenoid issues. No additive will fix that, only mask it.
If you're experiencing a thud or shudder during 1-2 or 2-3 upshifts, that is clutch plates and/or bands or possible servo and solenoid issues. No additive will fix that, only mask it.