Yes this happened with my LS430 i had to rev it higher than normal to start just like you and one day while on the motor way, when suddenly no drive. I pulled over and and no matter how much i revved the car, the car didn't move. It had to be lifted to a garage turns out after a service there was water damage into my gearbox or Gaerbox oil dirty or siezed, whole gear had disintergrated and i have now had to replace the gearbox it was a pain to find a gearbox which was affordable, So i had to buy a front end damaged LS with a good gearbox took about a year to get fixed.
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