Rather than continue on the six speed transmission thread that just closed. I thought I'd try to start a new thread with positive information. Mine is a difficult situation that began with brand new Tundra Double cab with transmission rumble @ 32-35 mph and 1200 rpm under acceleration. Already have one transmission replacement waiting for second round.
Dealer Service Director calls today to tell me a brand new Transmission is in route. More importantly, they think they have identified problem causing rumble. Toyota is still testing and compiling data using serial number tracking etc. Right now it appears there is an issue with how the torque converter is assembled and held in place in the transmission housing. Toyota has already implemented the change to correct the problem in new production transmissions. Supposedly, the way it is supposed to work, Once a fix is implemented all in stock units that have already been distributed are recalled and blocked from dealer use.
I am not sure I can express the exact details provided me by the dealer. Suffice to say his explanation made sense and it sounds like my truck will be soon on the road to recovery.
Most importantly I have rekindled hope and confidence in Toyota's exemplary reliability and fine service.