My ls400 95 (144000 mile) is right now at the Lexus dealer with this issue, this is the second dealership that will be looking at it. The first did not fix it because they could not reproduce it.
I drive it on the freeway every day.
When I drive it for a distance greater than 30 minutes, speeds over 65, brake at a right turning off ramp, idle goes down and it stalls. The car immediately starts back up. Drives fine on the city streets, no more stalling after restarting the car.
I get the "off throttle shock" as well. Thanks for giving me something to try.