Is it possible this is a PCM/engine issue and not a transmission issue? Maybe the RPM surge is being caused by a faulty 02 sensor or other PCM data and the symptom just feels like the TCC is unlocking/locking?

I'm no expert, but could be you're barking up the wrong tree here? One clue is the sluggish feeling from 65-70. Are you actually feeling any surging, or just seeing it on the tach? Could be a failing cam sensor or crank sensor that's providing fluctuating tach readings and affecting performance as well.