I just bought a 2012 Toyota Sequoia - it now has.

I just bought a 2012 Toyota Sequoia - it now has approx 1000 miles on it. There is a noticeable harmonic droning vibration at certain speeds (60mph for example) that can be felt through the floor boards, steering wheel, gas pedal The techs at the dealer said it is TCC problem. The Torque conversion converter is trying to go into lockup mode but the computer can't decide to lock it up or not at that speed causing it to go in and out rapidly which causes the shuddering or vibration. If I slow down or speed up the vibration goes away. The techs say this is normal and it may smooth out as the computer "learns" my driving. "It is an electrical issue not mechanical". I had a 2008 sequoia previous to the 2012 sequoia and never noticed this vibration. Is this a "normal" condition, I'm concerned that it will cause mechanical problems with the tcc over time? It's disappointing that an expensive car such as this has this vibration. Thank you