You're not alone. Mine has done this on occasion. I have to shift to S mode and shift up. Mine seems to do it in the same spot when it does happen, on my way home there is a slight hill. I go up it and on the way down it won't shift past 4th.

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2007 RCSB 5.7L w/ Sport package

Future Mods: JBA headers and TRD supercharger!
JBA Exhaust here, didn't fit!!!
Voalnt Intake ordered and on the way!
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Stock 07 Tundra 0 to 115mph. 60mph in 5.6 seconds