1. Make double dog sure that it's not an engine performance issue. I see tons of cars that have been diagnosed (in desperation) and with exactly this kind of symptom and they pass the buck to a faulty gearbox cos the Tech is sick of it and wants to give it a body swerve.

2. It's possible that the TC sprag assy is U/S, this makes the car really sluggish, the only way to prove it is to replace the TC.