ucf20 Jason

Im in need of some serious help. I have an LS400 which just hit 167k and trans service was done at 157k. I start the car it runs fine all the gears shift smooth but about 5 minutes after or once the car is completely warm none of the gears work anymore. I gas it to move and my rpms just go up. I turn the car off let it sit for alittle and it repeats itself. What can it be? Thanks in advance.