Our 2010 Toyota Tundra had similar automatic transmission problem ... earlier this year.
The 'rumble strip' shuddering noise appeared suddenly and continued randomly. The noise typically lasted about 5 to 20 seconds and sounded like the source was near the right front wheel. (I feared mud was embedded in front brake or bearings) After several more weeks driving, a pattern emerged that is almost exactly as described in some of the prior posts.
The noise was most evident when I was driving between 10 - 40 mph and on a slight uphill grade. That is when I realized the problem may be related to transmission shift points at varying speeds. If I go up the grade slowly, the shuddering noise appears. If I press the gas pedal a little harder, going up hill faster, the noise was less loud and shorter duration (sometimes no noise). I think the transmission was able to make the gear shift ... easier.
Solution: Took Tundra to a local Toyota dealer. I ask them to 'drain and replace' the transmission fluid. No, not a simple 'flush'. (Yes drain, in spite of the Toyota maintenance schedule that does not include transmission fluid replacement).
Drove away from dealership and problem was better ... but still there. After about 2 weeks more driving, shuddering noise and vibration ... faded away. Gone.
Since fluid replacement, I've driven Tundra round trip from central Texas to Denver; ~ 2000 miles. Absolutely no 'rumble strip' shuddering vibration or noise.
Replace the fluid. Toyota dealership charged about $180 or so.
Cheers !
